I seem to be having a similar issue. The really odd thing is some things in the system send emails, and some don't. Specifically:
- Backup summary email notifications come through each night (From noreply@xxx)
- Face to Face (plugin) reminders come through (From noreply@xxx)
- Face to Face (plugin) confirmations do not come through (no error)
- Password reset requests do not work (generates error)
- Forum emails come through (From noreply@xxx)
Would be interested to see if anyone else is having a similar issue.