Cannot send Mail - server error 451


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Would appreciate help/advice on the following error message:

An unknown error has occurred.
Subject 'Re: XXXXXXXXXXXXXXXXX' [I have X'd out the subject]
Server Error: 451
Server Response: 451 Invalid Smtp line - Should end with CRLF
Server: '' [I have X'd out the name of the ISP]
Windows Live Mail Error ID: 0x800CCC6A
Protocol: SMTP
Port: 25
Secure(SSL): No

Windows Mail was working but now error message above appears when SENDING. Will receive but not send from my account. Account details appear to me to be correct. No software changed as far as I know. Security (AVG) kept up to date. OS is Windows 7 Home Premium 64 bit. Laptop is only a few weeks old. Although I have been told error 451 points to ISP's server, the problem does seem to be at my end, and on this laptop as I can still send mails out on my Desktop PC through the same wireless router using the same server details and email account (though using Outlook 2003 on that machine. Thanks for reading this and for any help you are able to give. :hammer:


EQ Forum Admin
Staff member
Who is the outgoing mail server ISP?

The error points to a mail server doing strict CRLF checking, for example a qmail based smtp relay that is not running fixcrio.

Most mail programs don't send bare line feeds anymore so it's odd you have this problem with Windows Live Mail.

I do see this problem sometimes from Windows based web servers relaying out qmail based smtp relays.

That's the reverse situation though where fixcrio was required so that Windows could relay out email from web sites.

I'd start with the ISP that provides your smtp relay service and tell them to disable the bogus check.

If they think it stops busted spam bots, it really doesn't, and is likely doing more harm than good for their customers.

Feel free to link them to that opinion. :)

:welcome: to Email Questions!


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I had a similar probleml and figured out what was wrong. I removed the message referenced by the subject of the error and it worked. I suspect the message was formatted in a way that caused it to break.;)