First of all I wanna thank you for such a good Plugin! Using it for some time now and really like it!
Since of today I have a really strange issue though. I’m able to send emails (no error message) but the subscribers won’t receive them! So I checked and sending one with the “WordPress-only thing” works fine.
Already tried to change the sender, return path and reply to email addresses. Nothing works… The only thing I have in mind now is that my provider dumped PHP 5.2 and went to PHP 5.4! Could this be a problem?
Changes to PHP version SHOULD not interfere, since it is not a major release update. In the diagnostic panel, if you test the emails sent by Newsletter, none of them is delivered? Are you using the SMTP?