I have just started building a site which sends me mail from a contact form using a single private domain email address. When my site was http, all emails were going straight into Outlook and Gmail inboxes. I was debugging ajax POST therefore sending myself a flurry of emails which suddenly stopped, before I realised they got junked from the moment I switched on SSL.
Is there a good reason for this?
N.B. This isn't a question about configuring DKIM or general domain/IP trust, but specifically why email sent from a domain with SSL vs same domain on http might be deemed less trustworthy as the former.
After digging through example MIME sources I tracked the problem down to SPF auth timeouts. When testing I was switching between DNS record backups, one SSL and one non-SSL. This was caused by my non-SSL config not containing the SPF TXT record to gain authorisation for my mail forwarder. My bad.
Lesson: debug email issues with MIME source first