Some time ago there was a discussion of threading being broken in Apple Mail.
One of my users just reported this as having changed on our site, since we switched recently from SendGrid to Amazon SES.
It would seem that the problem is related to the Message-ID header being different. It doesn’t seem that it’s possible to override Message-ID on SES:
- Message-ID ( Note: Amazon SES overrides any Message-ID header you provide.)
Any other thoughts about how I might be able to get threading to work for my users relying on Apple Mail (which is most of them)?
@peternlewis. are you still having issues here? What email service are you sending through?