The ‘too many syntax or protocol errors’ response occurs within Outlook if you attempt to send an email to an improperly formatted address.

Task ‘Mailer – Sending’ reported error (0x800CCC0F) : ‘The connection to the server has been lost. If this problem continues, contact your server administrator or ISP. The server responded: 501 Too many syntax or protocol errors’

How can I fix it?

When you are sending emails using Outlook, ensure that the recipient address doesn’t contain any special characters, such as quotation marks around the address. The server won’t know how to handle this and will generate the error.

This error often occurs when you copy & paste an address into the ‘To’ field without removing the quotations (e.g., ‘name@website.com’ instead of just name@website.com).

Important! Delete the old mail from your outbox! And then to fix the problem, remove the quotations or any other irregular symbols and resend your email.

If our firewall blocked you from sending, please contact our support and send us your WAN IP address (click link for tools to search your IP address). Please note that if the above-mentioned email address isn’t fixed in your To/Cc/Bcc or contact list this problem will continue to occur!

Related source: https://clients.whc.ca/