Problem
The SMTP server returns the following error:

 

The SMTP host’s reply to the MAIL command was 501, but it was expected to be 250. The reply text was “5.5.4 Invalid Address”.

 

Cause
The email address may include Unicode characters. SMTP does not support non-ASCII characters in email usernames. For example, in myname@somewhere.com, myname cannot include Unicode characters.

 

Solution
Remove the Unicode characters from the email username and resend the message.