SMTP Email Error 501 5.1.3 occurs when the email address format is invalid or improperly structured. This error typically appears if the sender or recipient’s address contains incorrect characters, extra spaces, or missing elements like “@” or domain names. To resolve it, double-check the email addresses for accuracy, ensure there are no typos, and follow the correct email syntax. Adjusting server settings may also help if the issue persists.
SMTP Email Error 501 5.1.3: Fix Invalid Email Address Format Issues