Ask HN: Best practices for sending emails through web applications?

I know there's mailgun, sendgrid, or you could hook up external emails such as google app domain emails, or you could handle everything yourself e.g. IMAP.

I know there are pros and cons to each, and that a lot of the sendgrid-type sites try to scare you into thinking the mail will go to spam unless you use their services. Especially for cloud-hosted apps, with more complicated IP scenarios.

How much of that is truth? What do you use?

I'm sure this is a perennial question, but the landscape is also constantly shifting.

Thank you in advance!