Thanks for the reply Jeff. These are all things I thought of also, but here are some things that complicate the matter a bit.
- I rarely received a returned email before the update to 1.3.
- About 80% of the users signed up at a time when I had email verification on (email password on signup), requiring a valid email to access the boards. While it's possible perhaps even likely that some of these emails have since been closed, I doubt almost 800 of 1500 users have in a matter of 3 months.
- No PHP has been edited in terms of the email users option.
- Some of the transcripts of the returned mails said that "it is likely that the server did not like something in your header, or it looked suspicious"
- The email addresses were also in a valid format. (
[email protected])
-Evil-Eddy