They didn't really leave Mozilla, they formed MZLA Technologies Corporations which is a subsidiary of the Mozilla Foundation. Nonetheless, I agree that things have been drastically improving since the change.
Does it bring back the old, perfectly functional UI that everyone’s used for years? No? Hard pass. People don’t have the time to waste searching around for some button or menu item that the designers have moved somewhere else, buried in about:config or removed entirely. They force this ugly, garish mess of whitespace on us and tell us it’s the “most beautiful Thunderbird yet”. Maybe if enough of us cover our ears and clamp our eyes shut and shout that loud enough, it’ll become true. Me personally? I’m sticking with my trusty v102.12.0, thanks.
For what it's worth, I upgraded to 115. I can't remember how long it's been. I forgot I upgraded because it doesn't seem that different to me. I still have pretty small fonts and very little spacing around things. Above my reading pane are buttons with words on them like "Reply All" and "Forward." Some menus are still hidden behind an oddly placed hamburger near the top right, just like they were before. Search is still pretty mediocre!
I don't see what the fuss is about. They made rather minor changes overall and gave the app a bit of a facelift. I personally like the changes (for example putting the keyboard shortcuts in the search bars... I don't recall them being there so prominently, but I like the reminder when I forget, and it doesn't get in the way when I don't.) Regardless, we cannot let stagnation be the answer.
I think the only prominent UI change that happened is that the bar that holds the search box, Write button etc is above the tab bar now instead of below.
Personally, I find it a bit jarring, because contextually, that bar only contains stuff related to mail, but that bar and some stuff on it continues to appear even when I switch to Calendar. Thankfully, some CSS takes care of this.
Otherwise, it is a quite nice change. Dark mode now also applies to mail contents as well, which is a great change, though I would like a shortcut to swap to light mode.
It never occurred to me that I should not open a new window to compose an email. How would that work? Displace the folder I'm in, or the message I'm looking at? And why?
My Thunderbird window is not full screen but it's larger than the mail composition one. I can use that extra screen space to look at other things while I write a message. Short messages go through WhatsApp and Telegram nowadays. Outbound email is for important matters, so it's not uncommon to look at reference material. A tab wouldn't do.
Inbound email is 99.9% notifications. I read and delete most of them with K9 on my phone before downloading what's left with Thunderbird. BTW my mailbox is on a POP3 server. I clear it after downloading the messages.
After the big update I had to spend an hour restoring it to a functional state including changing an about:config parameter to get the scaling right. Out of the box I got changes that broke my UI and no "beautiful" new UI to begin with (you need to actively change settings to convert). Also there is still a giant clonky Win98 scrollbar on my folders, so getting that clean look in the marketing screenshots is impossible unless I severely reduce folders so I don't need the scrollbar. Why the scrollbar wasn't replaced with something more modern? No clue.
And many people complained about the UI feeling dated before the change.
The new UI has a compact mode, I think you can get an even more compact UI than before. I've used thunderbird forever and I'm not lost at all. I think they did a really good job not breaking us.
I guess they can't please everyone but I don't know how they could have done better in this respect honestly.
There were several minor amateur moves however. The menu bar in the wrong place for example—not sure what they were thinking. Also hardcoded the highlight color to blue (on purpose), disrespecting the system UI theme. Same thing happened ~twenty years ago with firebug and I was happy to drop it for FF dev tools.
Every few years a new batch of "senior" engineers needs to earn xp points.
I could not disagree more vehemently. The old UI was ugly and clunky and anachronistic. I find the new UI much more readable, with a sensibly usable three-column layout, and much improved message list.
K-9 Mail joined Thunderbird to become Thunderbird Mobile [0]. They regularly publish progress updates [1] and their GitHub repository is regularly publishing releases and merging fixes and features [2].
What exactly do you want synced? Shouldn't the two mail clients just sync with your mail server individually? If you send an email from desktop, it will land in the sent folder, which the mobile client will then sync and show.
settings, calendar, tasks, contacts, I have multiple mail accounts and a lot of info that reside only on my main PC currently, I estimated that redoing everything would take hours to me.
One feature I'm missing is the ability to display 3 lines (from, subject, and the first line of the body) in the message list. When dealing with monitoring and certain notifications, I have to open each email to see its contents.
It’ll come in a future release. What you need to keep an eye out for is improvements in the “Cards View”. Currently it shows only the sender name, time and subject of the email. Quoting from the Thunderbird Supernova FAQ [1]:
> Cards View is still in active development. More features such as a message preview line and sender avatars will be added in the future.
I'm pretty happy with Thunderbird. Apple's latest "Mail" app is good too but I still use Thunderbird.
I just checked and mine says "115.3.3 (64-bit) Thunderbird is up to date" so I guess I'll be waiting a bit for the update but I haven't run into any of the issues they cite so I'm in no hurry.
Different background color for different accounts is the literal deal-killer for me here. Am I missing something? If not a basic built-in feature, this seems like this ought to be trivially easy as a plug-in, but they appear to have broken it?
"Canary Mail is an email client that offers artificial intelligence (AI) capabilities backed by technology from OpenAI & Cohere, as well as open-source language models from Hugging Face [...] Canary Mail flagship feature, Copilot, leverages artificial intelligence to help users write, summarize, and prioritize emails. The app's free version offers basic features, while the Pro Version, starting at $20 per year, offers additional features, including Copilot"
OMG I'd genuinely pay more not to have any of that, ever. I'm afraid CM is not an option, but thank you anyway.
It was very good in POP3 times, then lack proper IMAP4 support for several years, but now authors claim that IMAP4 support is first-class.
It is very old (first release in 1997) client with very-very old-skool features, like different templates with multitude of variables (and not only one option "where to place your signature") and rules to apply them (you could have different templates for different correspondents, you have different templates for new message, reply, reply to all and forward, etc, etc, etc). Built-in filters are rather good too, with a lot of automation.
But it looks dated, and HTML support is not the best. And there is no manage sieve client.
Not pretty out of the box but for what it’s worth I’ve got mine set up with my favorite fonts across the board, a customized Monokai Pro color scheme, and a custom widescreen correspondence layout.
Not to mention the lovely Bold, Italic, and tag-specific color-highlighting I’ve got going.
I sometimes dream that Mozilla would somehow convince Microsoft to make it easier to use Thunderbird with Outlook365. Many companies that use Outlook365 disable IMAP and SMTP entirely even though Thunderbird supports IMAP and SMTP with OAuth2. Microsoft has spread enough FUD to convince its customers that Outlook is the only client to be allowed and actively encouraged disabling “legacy protocols” for “security reasons”.
Thunderbird doesn’t support the Microsoft specific Graph API. While there are some extensions that could enable working with Outlook365 using some kludgy approaches, it would be better to have that natively supported.
That KB article is outdated. About Thunderbird: “Available cross-platform, it is operated by the Mozilla Foundation's subsidiary MZLA Technologies Corporation.” [1]
Nothing prevents Thunderbird from implementing the Exchange protocols. Many have done it, including Evolution, an open source competitor to Thunderbird.
The last couple major updates to Thunderbird have been really nice. I had to follow some tutorials they put out to get the UI better (stuff like Unified folders, tags, the different view settings, etc), but once I did it's been a really nice experience.
Absolutely agree, the new design makes it so much more modern & easy to use for the average user.
I have the feeling that many complaints here are about specific workflows or specific advanced features, but instead of trying to please everyone by doing everything MZLA has built a really nice email client that just works for the majority of its users and now is in a shape where it might even attract new ones.
Duplicate toolbar buttons (on main toolbar & account toolbar) are ridiculous.
But all of that could be tolerable.
What is NOT tolerable is broken "Manually sort folders" plugin.
Thunderbird sorts folders in tree alphabetically and only alphabetically, and it is pure nonsense! But before this update there was very handy plugin to rearrange folders in away you need, not alphabet needs. Now it is broken and author says that internal API is completely changed.
This is essential feature, IMHO. "The Bat!" mail client has this feature in, I don't know, 2000? With handy keyboard shortcuts (Ctrl+Arrows) too!
> What is NOT tolerable is broken "Manually sort folders" plugin.
I sadly agree with you. I'm waiting for some good news from the GitHub page of the plugin. My workaround is to mark as favorites the parent folders of the trees for my customers and place the favorites at the top of the tree list.
I never used favorites before, there was no need for them.
Ah yes, manually setting opaque CSS to revert an idiosyncratic UI design choice back to something that people would normally expect to see. Great, thanks.
Seriously, when I saw the "115 vs 102" slider thing on the website, I was surprised and disappointed to realize that that I instinctively interpreted as the new and improved UI was actually the old UI that I was already used to, and the weird iPad-esque thing was actually the new and supposedly improved UI that I was about to get. This is what I donate every month for? It's enough to make me reconsider my contribution.
>Thunderbird sorts folders in tree alphabetically and only alphabetically
Except when it doesn't. Personally, alphabetically is the way that I want it sorted, but sometimes Thunderbird starts up and the folders are randomly sorted, and I can't sort the back. I just have to close Thunderbird and start it again to get my folders back in the right order.
Thunderbird also lost the ability to have threads auto collapse for a while there (it seems to be back now?). So any long threads were auto expanded. Felt kinda like supernova was so heavily focused on "the redesign" that it failed to consider basic usablilty
Local copies of all the different webmail accounts and ability to search through that massive information overload in a unified way. What else can one possibly ask? Maybe some local AI to help sort out things just bit more :-)
Its a blessing that the project keeps going strongly.
Often, though I know exactly the info required to find a message, Thunderbird comes up with no results. I've found that "repairing" the containing mailbox renders the message findable.
Not sure when things got this bad, but I can well recall in the past Thunderbird's search being fast, thorough, and reliable.
Quick search is where it's at. Keeps the view sane and you select which fields to search (subject, recipients, body), the downside is that you have to know which folder to look in, which can also be an upside to narrow it down (I know that's also possible in the search UI but this is easier)
After couple of years of not using Thunderbird (I switched completely to web portals) I tried it when they released Supernova and all I can say is that it's... slow. Really, I often have UI freezes, data doesn't appear immediately, downloading mails take a lot of time, calendar also is not that snappy. I somehow expected to have everything super fast as it's a local app (after all the data is downloaded), but it clearly doesn't handle large amount of mails efficiently.
It runs well enough on my desktop, but on my tablet (SP9 with an i7...), each action has 1-2s latency. Ie selecting a new email, opening a compose window etc.
We need a from-scratch desktop email client that is fast and streamlined. I give on Tbird. At least in this version I can figure out how to disable the HTML email formatting and MS-word-style auto-spacing below paragraphs when composing.
Same. I opened Thunderbird recently after probably over a year and this switch to a browser rendering engine. The entire application locked up while it was updating my list of emails. I’m glad the project is seeing some FOSS love but it also seems to have gone down the entirely wrong path in pursuit of modernization without benefit.
Sadly for Linux there aren’t really any great modern UI-style (not browser rendering modern but just the look) email clients so I’ll just keep using my browser since there is now no benefit to using Thunderbird.
Oh and this is a brand new machine I built in 2022. So it’s not the hardware.
Over the last few months Thunderbird has got noticeably slower for me. When I click on the 'sent' folder for one of my email accounts I now have to wait ~30 seconds for anything to happen. Previously it was pretty much immediate. Not sure if I can change a setting to speed it up.
I entered to say the same. Not only Supernova. I purchased a Thunderbird based client (Postbox) in thehope that they solved the sluginess and...same problem.
Also, I have the feeling that the Windows version is slower than the macOS one.
It always was slow with larger mailboxes, taking a few seconds to react to a click (and sometimes freezing for minutes to move a bunch of emails ti a different folder).
I can’t tell if it’s any slower with Supernova or not. Feels about the same, to be honest. I suspect its bottlenecks are somewhere else.
On my computer it is much slower now. It was always slow on large mailboxes but now it is almost unusable and I am thinking about downgrading or switching. Any recommendations?
Are you using POP3 or IMAP? In my experience thunderbird on IMAP has always been very slow whereas I have no problem on my 2012 laptop with 30k emails when using POP3.
I do that from time to time. The issue is that the performance got worse with the new UI and that cannot be due to compacting. Will try to do it again though to see how much it helps.
My laptop is 5+ years old, and while TB is not the snappiest GUI app on the machine, performance is decent/acceptable. I welcome any optimization however.
The vacuuming is important on an older install I suspect.
I have used Thunderbird for years and my work account has to handle large numbers of emails. In general it is fast for me on both Windows and Linux. I have had some issues over the years but they normally turned out to be due to corrupt mail folders.
For me on Linux the change made it _way_ faster, like 5x faster. The previous releases were systematically slowing down, but now it feels fast like around 5.0.
I don't like where they put the new message button (it's weirdly floating over the list of folders now, but what's the relation with that list?). There's also a mostly empty bar _above_ the menu bar (I'm old-school, I like menu bars). It wastes space, looks silly, and cannot be turned off as far as I can tell...
I used to have an extension installed ("Mailbox Alert") that provides different notification sounds depending on the account receiving an email, but unfortunately that is now broken. That's a significant step back.
Thanks, but that still amounts to "no." If there's no menu item for this basic feature, it's not a function offered by the application.
Expecting the user to search the Web for how to do this and then dig around in data files that are buried in platform-dependent application directories is a hokey and not-production-quality "solution."
If it's just a data file, there's no excuse for neglecting its import and export (AKA simple copying) for 25 or more years. I mean, how did filter functionality even go out the door without this? They expect people to run around and manually re-enter all of their filters on every computer they own? And to do this perpetually?
With all due respect, Thunderbird is a FOSS project, which is largely run on unpaid volunteer efforts. I think it's quite right to denigrate their efforts because they didn't manage to build a particular feature.
I respect all the people who give an incredible amount of time to these projects. I help when I can, and give money to the ones I rely on when I can't contribute any other way.
But I heartily disagree that criticizing the product or the development priorities is "denigrating" their efforts. It is simply criticism, hopefully constructive. People were asking to copy filters between machines 20+ years ago. Filters are essential for any E-mail client; I can't imagine what the intended M.O. is for them in Thunderbird at this point.
If I weren't exclusively on Macs every day I would absolutely implement this myself; as it stands, I can't justify the time. But I can armchair-quarterback the shit out of it!
There is an export/import for settings, and it says to also include filters. Basically it seems to just zip your whole profile, so somewhere in that mess will also be your filters.
The main issue I have with Supernova is when I move into the Sent folder its focus is on the middle of the stack instead of the last e-mail I've sent. I just don't understand how something that essential slipped in the final version. The whole UI seems like it's half baked.
The calendar has been broken for a while now. It is impossible to close reminder popups, neither button does anything. It doesn't sync properly anymore either. I wish there was undo when you accidentally click the subject header and it sorts by subject. It is really hard to get back to sort by date then unread.
I don't use the calendar integration, but the behavior you're describing is almost certainly some JS explosion that wasn't handled. "Tools > Developer Tools > Error Console" (Ctrl-Shift-J in my copy) may cough up something that would enable you to file a bug report, if you were inclined, or may even help understand what expectation it had that your setup deviates from
This is not everyone-friendly answer, but Mutt does it. To the second point it's not even optional for composing. Unless you write/use some markdown to text/html.
Thunderbird has a very useful feature: simplified incoming html view. It strips remote images and js, while keeping the minimum to make messages readable.
Responses can use plain text.
I really liked Mutt. I used it for one or two years, a long time ago.
You can pipe text/html to w3m/elinks to get the same results. Well, almost the same, some e-mails are not that well designed. I still love mutt, it's so rapid and it works almost the same when I first used it, over 20 years ago.
mutt does both things. I've been using it for years. The learning curve is certainly steep, and being in the terminal all the time might throw people off, but it does what you're asking for.
I've used many, but that's ancient history. For a long time I used webmail and only Thunderbird in recent years. News of an interface revamp were scary, but so far no serious breakage. I guess people's complaints are about very heavy mailboxes or, most likely IMAP.
That is a different way of thinking: email as sort of a database of personal information, integrated with calendar and contact manager. If you're like me, only mail and not a lot of it, Thunderbird will be probably fine.
Not a GUI, but I am using neomutt which requires a bit of config and time to get used to. Thunderbird kept crashing for me every time i try to sign an email but i have no problems with neomutt.
I gave up and mostly use the Fastmail web UI. It's substantially better than Thunderbird and just about every other email client I've tried. But of course this isn't any help if you're not a Fastmail customer.
I'm really glad TB exists and is still developed. I try it once a year every year because I use Firefox, and TB is cross platform.
Honestly, I can't say it fits my needs more than Mac mail.app or the web client when on a windows computer (mailbox.org). I guess what I'm saying is that I have never used Outlook so I've never needed an open source replacement for it.
137 comments
[ 3.2 ms ] story [ 226 ms ] threadI personally never like the old UI, and though it still has ways to go, it's miles ahead of the old UI.
Personally, I find it a bit jarring, because contextually, that bar only contains stuff related to mail, but that bar and some stuff on it continues to appear even when I switch to Calendar. Thankfully, some CSS takes care of this.
Otherwise, it is a quite nice change. Dark mode now also applies to mail contents as well, which is a great change, though I would like a shortcut to swap to light mode.
1. the designers never considered keyboard navigation, which is now even more awkward than it was already
2. the interface is now very visibly slower - startup and general usage (on two of my systems)
This ignores the very long standing issues like:
1. searching is very confusing; there are several different types of searches
2. writing an email still requires opening another window. compose emails like it's the 90s!
Inbound email is 99.9% notifications. I read and delete most of them with K9 on my phone before downloading what's left with Thunderbird. BTW my mailbox is on a POP3 server. I clear it after downloading the messages.
The new UI has a compact mode, I think you can get an even more compact UI than before. I've used thunderbird forever and I'm not lost at all. I think they did a really good job not breaking us.
I guess they can't please everyone but I don't know how they could have done better in this respect honestly.
There were several minor amateur moves however. The menu bar in the wrong place for example—not sure what they were thinking. Also hardcoded the highlight color to blue (on purpose), disrespecting the system UI theme. Same thing happened ~twenty years ago with firebug and I was happy to drop it for FF dev tools.
Every few years a new batch of "senior" engineers needs to earn xp points.
To each their own, I guess.
0: https://blog.thunderbird.net/2022/06/revealed-thunderbird-on...
1: https://blog.thunderbird.net/category/thunderbird-mobile/
2: https://github.com/thundernest/k-9/pulse
(Well, okay, there's sieve, but server support for sieve is kind of spotty, and most clients don't try to map their filters to sieve filters.)
> Cards View is still in active development. More features such as a message preview line and sender avatars will be added in the future.
[1]: https://support.mozilla.org/en-US/kb/thunderbird-115-superno...
I just checked and mine says "115.3.3 (64-bit) Thunderbird is up to date" so I guess I'll be waiting a bit for the update but I haven't run into any of the issues they cite so I'm in no hurry.
No seriously, it was an easy plugin. Then they broke all the plugins, and I'm legit -- why should I care about this as "open-source" again?
"Canary Mail is an email client that offers artificial intelligence (AI) capabilities backed by technology from OpenAI & Cohere, as well as open-source language models from Hugging Face [...] Canary Mail flagship feature, Copilot, leverages artificial intelligence to help users write, summarize, and prioritize emails. The app's free version offers basic features, while the Pro Version, starting at $20 per year, offers additional features, including Copilot"
OMG I'd genuinely pay more not to have any of that, ever. I'm afraid CM is not an option, but thank you anyway.
It was very good in POP3 times, then lack proper IMAP4 support for several years, but now authors claim that IMAP4 support is first-class.
It is very old (first release in 1997) client with very-very old-skool features, like different templates with multitude of variables (and not only one option "where to place your signature") and rules to apply them (you could have different templates for different correspondents, you have different templates for new message, reply, reply to all and forward, etc, etc, etc). Built-in filters are rather good too, with a lot of automation.
But it looks dated, and HTML support is not the best. And there is no manage sieve client.
Edit: Windows only.
Not to mention the lovely Bold, Italic, and tag-specific color-highlighting I’ve got going.
Thunderbird doesn’t support the Microsoft specific Graph API. While there are some extensions that could enable working with Outlook365 using some kludgy approaches, it would be better to have that natively supported.
https://support.mozilla.org/en-US/kb/thunderbird-faq#:~:text....
Also see [2] for how this came about.
[1]: https://en.m.wikipedia.org/wiki/Mozilla_Thunderbird
[2]: https://blog.thunderbird.net/2017/05/thunderbirds-future-hom...
https://www.exquilla.com/
I have the feeling that many complaints here are about specific workflows or specific advanced features, but instead of trying to please everyone by doing everything MZLA has built a really nice email client that just works for the majority of its users and now is in a shape where it might even attract new ones.
Duplicate toolbar buttons (on main toolbar & account toolbar) are ridiculous.
But all of that could be tolerable.
What is NOT tolerable is broken "Manually sort folders" plugin.
Thunderbird sorts folders in tree alphabetically and only alphabetically, and it is pure nonsense! But before this update there was very handy plugin to rearrange folders in away you need, not alphabet needs. Now it is broken and author says that internal API is completely changed.
This is essential feature, IMHO. "The Bat!" mail client has this feature in, I don't know, 2000? With handy keyboard shortcuts (Ctrl+Arrows) too!
There is way to undo that, at least on Linux.
Edit or create the file chrome/userChrome.css in your profile directory and add
Restart Thunderbird. Maybe it works on all OSes.Credits to https://superuser.com/questions/1787317/thunderbird-114-115-...
> What is NOT tolerable is broken "Manually sort folders" plugin.
I sadly agree with you. I'm waiting for some good news from the GitHub page of the plugin. My workaround is to mark as favorites the parent folders of the trees for my customers and place the favorites at the top of the tree list.
I never used favorites before, there was no need for them.
Seriously, when I saw the "115 vs 102" slider thing on the website, I was surprised and disappointed to realize that that I instinctively interpreted as the new and improved UI was actually the old UI that I was already used to, and the weird iPad-esque thing was actually the new and supposedly improved UI that I was about to get. This is what I donate every month for? It's enough to make me reconsider my contribution.
Except when it doesn't. Personally, alphabetically is the way that I want it sorted, but sometimes Thunderbird starts up and the folders are randomly sorted, and I can't sort the back. I just have to close Thunderbird and start it again to get my folders back in the right order.
Its a blessing that the project keeps going strongly.
Often, though I know exactly the info required to find a message, Thunderbird comes up with no results. I've found that "repairing" the containing mailbox renders the message findable.
Not sure when things got this bad, but I can well recall in the past Thunderbird's search being fast, thorough, and reliable.
Quick search is where it's at. Keeps the view sane and you select which fields to search (subject, recipients, body), the downside is that you have to know which folder to look in, which can also be an upside to narrow it down (I know that's also possible in the search UI but this is easier)
We need a from-scratch desktop email client that is fast and streamlined. I give on Tbird. At least in this version I can figure out how to disable the HTML email formatting and MS-word-style auto-spacing below paragraphs when composing.
Also, search still doesn't work for me.
Sadly for Linux there aren’t really any great modern UI-style (not browser rendering modern but just the look) email clients so I’ll just keep using my browser since there is now no benefit to using Thunderbird.
Oh and this is a brand new machine I built in 2022. So it’s not the hardware.
Also, I have the feeling that the Windows version is slower than the macOS one.
I can’t tell if it’s any slower with Supernova or not. Feels about the same, to be honest. I suspect its bottlenecks are somewhere else.
I have mail back to the mid-nineties and it works fine, besides a few UI glitches from the new version. (There are buttons that can't be removed.)
The vacuuming is important on an older install I suspect.
That being said, I haven't found a better alternative yet...
A bit surprised that there aren't really any other strong competitors in the space.
I used to have an extension installed ("Mailbox Alert") that provides different notification sounds depending on the account receiving an email, but unfortunately that is now broken. That's a significant step back.
This glaring and baffling omission was a deal-breaker 25 years ago.
[1] https://support.mozilla.org/en-US/questions/1269514
Expecting the user to search the Web for how to do this and then dig around in data files that are buried in platform-dependent application directories is a hokey and not-production-quality "solution."
If it's just a data file, there's no excuse for neglecting its import and export (AKA simple copying) for 25 or more years. I mean, how did filter functionality even go out the door without this? They expect people to run around and manually re-enter all of their filters on every computer they own? And to do this perpetually?
But I heartily disagree that criticizing the product or the development priorities is "denigrating" their efforts. It is simply criticism, hopefully constructive. People were asking to copy filters between machines 20+ years ago. Filters are essential for any E-mail client; I can't imagine what the intended M.O. is for them in Thunderbird at this point.
If I weren't exclusively on Macs every day I would absolutely implement this myself; as it stands, I can't justify the time. But I can armchair-quarterback the shit out of it!
Do you think the complaints posted in this thread aren’t because code was rewritten?
1. Supports GPG signing and decryption
2. Allows plain text views and composition to be set as default
I use ThunderBird for those two specific reasons, and I'd be fine trying something new too.
+ Bottom posting can be set as default.
+ Selected text are automatically quoted when hitting reply.
+ Many add-ons and utilities are available: DKIM verifier, Mail Hop viewer, Mail Agent viewer, etc.
I tried to find an alternative but I couldn't either.
Responses can use plain text.
I really liked Mutt. I used it for one or two years, a long time ago.
That is a different way of thinking: email as sort of a database of personal information, integrated with calendar and contact manager. If you're like me, only mail and not a lot of it, Thunderbird will be probably fine.
https://en.wikipedia.org/wiki/Gnus
Honestly, I can't say it fits my needs more than Mac mail.app or the web client when on a windows computer (mailbox.org). I guess what I'm saying is that I have never used Outlook so I've never needed an open source replacement for it.
https://bugzilla.mozilla.org/show_bug.cgi?id=449299