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revup67's avatar
New Contributor

Error: undeliverable: Server error: '550 5.1.1 relaying not allowed

this issue just began.  I simply reply to an email address I have been for years with the same mail client Outlook 2010 and out of nowhere the message immediately gets returned by the System Administrator say Server Error undeliverable: Server error: '550 5.1.1 relaying not allowed'

Note, there is no hexadecimal error code.


Solution:  in Outlook go to the Account Settings (which should be off the File Menu though there are many version of Outlook and the version you have may be different if so use the question mark or help menu to search account settings), then select the Cox account having issue.  Choose "Change" then "More Settings".  Look for the tab that says "Outgoing Server".  At this tab check the box that shows MY Outgoing server requires authentication".  The radio button below this "Use Same Settings..." will also be selected.  Click OK then Next and the test message should complete in both directions incoming and outgoing successfully.

The reason this has occurred is due to Cox cracking down on Spam Mail.  By including these settings it tells the Cox server you have an account with a proper password.  If you call Cox support they will insist its an Outlook issue despite the Server Message


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  • DerrickW's avatar
    Valued Contributor
    Hi, are you currently away from home trying to send email? That error usually occurs if you're using our outgoing mail server with a different ISP; you would need to set the outgoing mail server to authenticate.
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