Delivering mail in Drupal 8
The idea of sending mail is to get it to the end user and get them to read it right? We'll talk about the first part of that, sending, but also how to make sure it gets all the way there and (hopefully) doesn't just end up being tossed.
* Sending email from code
* Building the body array in hook_mail()
* Altering email sent by another module
* Development environments and debugging
* Production environments: Clean IPs, SPF, DKIM
* Mail services like Mandrill and Sendgrid
* Swiftmailer, Mail System, and HTML Email
@trobey pointed out the excellent service from port25.com: Send an email from your site to firstname.lastname@example.org and you'll get a reply with a complete analysis of SPF/DKIM results and many other things (example). Excellent.