I've started getting an error on my windows machine when sending an email through Windows Mail, using Mobile Me:

An unknown error has occurred.

Subject 'Test' Server Error: 503 Server Response: 503 5.7.0 TLS already in use. Server: 'smtp.me.com' Windows Live Mail Error ID: 0x800CCC65 Protocol: SMTP Port: 587 Secure(SSL): Yes

I've checked and double-checked my credentials, and outbound mail settings, and they're correct. I've deleted and re-added the account, and I get the same issue.

I'm able to receive email fine.

Note - this issue only affects one PC - my laptop has no issues.

Any suggestions on what Error 503 means, or how I would fix this?


Turned out to be caused by Avast AntiVirus. I suspended email protection, and outbound emails started sending again.

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Look at smtp error 503 in this document for detailed information about what it means. In general it means there is an issue with authentication, either it is not passing and the email is being rejected, or it is being interrupted (say though an intermittent connection, or maybe you are on a poor wireless connection), and is being rejected because authentication can't complete.

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