Outlook Error 501 Too many syntax or protocol errors

One of the more common errors you may encounter when using the Outlook email client is the 501 Too many syntax or protocol errors error. It can occur in combination with other Outlook errors, for example together with error 0x800CCC0F, 0x800CCC78 or 0x8004210B.

As you can see in the image above, a warning is displayed when sending an email fails:

Task 'email@vasadomena.si - Sending' reported error (0x8004210B) : 'The operation timed out waiting for a response from the sending (SMTP) server. If you continue to receive this message, contact your server administrator or Internet service provider (ISP). The server responded: 501 Too many syntax or protocol errors'

It is also possible to get one of the following errors:

Task 'Mailer - Sending' reported error (0x800CCC0F) : 'The connection to the server was interrupted. If this problem continues, contact your server administrator or ISP. The server responded: 501 Too many syntax or protocol errors'.

The following recipient(s) cannot be reached. Server error: '501 'email@vasadomena.si': malformed address: '> may not follow 'email@vasadomena.si''

The message cannot be sent. Please check the email address in the account properties. Server response: 501 'email@vasadomena.si' SMTPUTF8: malformed address: SMTPUTF8 may not follow 'email@vasadomena.si'

Why does the error occur and how to fix it?

In most cases, the Outlook error 501 Too many syntax or protocol errors is related to the writing of an illegal character in the email address to which the message is addressed.

Most often it is:

• quotation mark: ‘ or “
• broken brackets: < or >
• square brackets: [ or ]
• an elided consonant: č, š, ž

The correction is therefore quite straightforward. Check the spelling of the recipients of your email message and remove special characters.

The special characters are not accepted by the email server, so the message cannot be sent successfully.

If you have any further questions, please call us on 059 335 000 or email us at info@neoserv.si.