Hi Boston,
I've just started to have the same/similar problem.
The shop has stopped sending order/account creation confirmation emails & when users register for a newsletter they don't receive the activation email.
Newsletter are being sent out.
All this worked until 11/4. For a time even the newsletters weren't being sent but then they did start working again.
The config for this shop is the same as 2 others on the same server - these are not having a problem. I've also checked the admin activity log just to make sure that the store owner has changed any settings - which he hasn't.
zc 1.3.7 Php 4.4.7 Zend 1.3.0 (mail protocol PHP).
This seems to point to a server issue except that the other shops are OK. The client's email goes via another provider's email filtering (domain thus has a separate MX record) & I've checked that this server isn't blacklisted.
The only change that has been made to the shop (by me) was to disable phpBB linkage by setting the value to false in the My Shop admin section. I doubt that this would have any effect but I'm getting a bit desperate!
Any suggestions/thoughts would be most welcome.
Thanks,
Eddie