Outlook error 0x800CCC6A with 451 "invalid SMTP - 'should end with CRLF'

I'm able to successfully send and receive emails, with or without attachments, but with each initiation of the 'send/receive' cycle I get the above error.  If I repeatedly initiate the 'send/receive' process, even when there are no actual messages being transacted in either direction, it always shows that 4 messages are trying to be sent.

My Outlook interfaces with my Ameritech ISP email account. I've looked at the web server to see if there might be some 'trapped' emails but haven't found anything. I've checked my outgoing mailbox and there are no 'trapped' messages there either.

Hope that someone has some ideas about how to resolve this.


See if you have undeliverable read receipts: Delete a stuck Read Receipt.
Brian Tillman [MVP-Outlook]
If a reply helps, please vote it as helpful. If a reply solves the issue, please mark it as an answer.

1 person was helped by this reply


Did this solve your problem?

Sorry this didn't help.

Great! Thanks for marking this as the answer.

How satisfied are you with this reply?

Thanks for your feedback, it helps us improve the site.

How satisfied are you with this response?

Thanks for your feedback.


Question Info

Last updated July 22, 2020 Views 3,548 Applies to: