SMTP Error: Data not accepted

[shadowplayfg2]

 

I am having an issue with the outgoing email addresses for the support departments we created. Each of the department is setup to use POP3 to import the emails directly to WHMCS based on the cron job.  We also have SMTP setup for one email address on the general settings. There is only a single username we can setup on the SMTP option.

When we receive emails directly to say to our support or billing departments,  the emails would import correctly into WHMCS.  When we reply to the tickets, only 1 email address would work and all others would generate the below error message:

Admin Email Notification Sending Failed - PHPMailer Exception - SMTP Error: data not accepted. (Subject: POP3 Connection Error)

I'm wondering if this is due to the single username we have setup on the SMTP settings and it is trying to authenticate based on the outgoing sender email address?

 

Thanks

[shadowplayfg2]

actually its this error message:

 

Email Sending Failed - SMTP Error: data not accepted. (Subject: [Ticket ID: 942446] Test Test)