Emails failing with Error 12206 Server transaction failed

We are getting the error below in Munis:

The utility program (sendmail.wsf) generated an error. 

ERROR: 12206: Server transaction failed

Recipient(s) xxxxxxuser@emaildomain.com From: xxxxxx@emaildomain.com

Calling SocketTools SMTP Connect method.

• Munis
• W-4 processing
• Email 
• SMTP

The SMTP server user being used for the SMTP connection is missing send as permissions.

1. Navigate to System Administration > General Administration > System Settings
2. Select the Email tab
3. Obtain the SMTP server user ID
   1. Note: This must a real email address (not distribution group) that can send email
4. Assign user Send as permissions through the SMTP server

https://learn.microsoft.com/en-us/microsoft-365/solutions/allow-members-to-send-as-or-send-on-behalf-of-group?view=o365-worldwide

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