There are two issues in this thread.
1. Emails not being sent
@Ripplestone has applied a fix for emails not being sent.
I've come across this issue on some Windows IIS servers running WordPress not being able to properly send SMTP mail.
Never had a problem with Linux servers.
2. Incorrect format in Email header
@midexsoftware is correct.
There is a problem in the way the outgoing SMTP email is formatted.
It is trying to send out the email using the admin email address in the plugin settings, however, the actual email address in the header is still being recorded as your WP system email (General > Settings).
This is causing some email systems to mark the email as suspicious as it looks like somebody is spamming the From address.
For those who say they are not receiving emails, I would suspect you are but that they are being sent to a SPAM/Junk folder on your systems or being rejected by a SPAM/Junk email filter on your mail server.
Please check both systems if this is the case.
TO THE DEVELOPER:
Please fix this and correctly format the outgoing SMTP email.