I have a customer using my server as their relay for their website. If I send a test email with HTML it fails. If I uncheck the use HTML and send the email in plain text it works fine.

The web server will send the form using my mail server's user accounts and settings as the relay.

It looks like it is going to write to the email file, then it gives an error: data transfer failed

I need to figure this out soon or look for another mail solution. Cannot afford to lose another customer.

After reviewing it and do some more testing I decided to just create a ticket. I can send emails using my cPanel server no problem, SmarterMail fails. I lost a customer and now realized it was a bigger issue than I first thought.