email is absurdly involved if you want to make sure that gmail etc. accept your messages as non-spam.

I've self-hosted DNS, mail, web, etc. for years, and several people have posted the same kind of comment here, so here's what people will need to know/do to self-host their own mail.

First, you'll almost surely need a non-end user IP address, as many/most of such address ranges are in the Spamhaus PBL list [0]. To see if your IP address is listed in PBL, for the example IP address 192.0.2.200, do

dig 200.2.0.192.pbl.spamhaus.org

Here, the octets are reversed and prepended to pbl. While you're doing this, you may as well also do

dig 200.2.0.192.zen.spamhaus.org

Again, replacing the above IP address with your own. This checks the Zen list [1].

For a non-end user IP address you'll most likely need a datacenter machine, a business line, a VPS, or a machine hosted at a large organization. A home Internet connection won't cut the mustard for mail.

Second, you'll need FCrDNS [2], or at least rDNS. rDNS is just short for reverse DNS, which means having a PTR record in DNS for your IP address. It could be anything, but something non-generic is best, such as mail.example.com, or puffy.example.com. wireless-cust-0-200.example.com is generic and will score "bad" points on some remote systems.

It's best if you can do FCrDNS, which is trivial. All that entails is matching PTR/A records.

This is all you need for Gmail or any other serious mail provider to accept your mail. Unfortunately it makes self-hosting from home more difficult, but the upside is a huge reduction in spam.

Last thing, you should check http://dnsbl.info or a similar site to see if your mail server's IP address is listed in any DNSBLs.

0. http://www.spamhaus.org/pbl/ 1. http://www.spamhaus.org/zen/ 2. https://en.wikipedia.org/wiki/Fcrdns