One day, just randomly, Apple mail stopped sending outgoing mail. By random, I mean random. There was no OS upgrade, no quit and restart mail it just stopped working. After two hours on chat with my hosting company’s support, I still didn’t have a resolution.
Emails were backing up and I was trying to work around it. The third attempt at live chat resulted in the tech saying (offhandedly) oh yeah, a lot of people have problems with Apple mail, it’s just unstable. He then suggested I use Outlook (is that Outlook or Entourage? either way, never going to do that) or another email program.
This led to me downloading a few different programs and purchasing Airmail2. Airmail2 and I were off to a really bad start, it wouldn’t import my accounts from Mail, their support never answered and I never could quite get the hang of it. Not to mention I had to re-do all my Spam Sieve filters and they still weren’t working properly.
Miserable. 3 weeks later and I was miserable and determined to fix it.
In my situation, Apple Mail ONLY had an outgoing mail issue. And I knew it had SOMETHING to do with my hosting company in particular. It hit me that with Mandrill you get thousands of outbound emails on their free plan and I signed up but never used it. I logged into Mandrill, grabbed the SMTP information, plugged it into Apple Mail and was back in business. Problem solved. You can probably also do the same with SendGrid.