I was having problems sending email through my ISP earlier this week. The error message I was receiving from Outlook Express was
Your server has unexpectedly terminated the connection. Possible causes for
> this include server problems, network problems, or a long period of
> inactivity. Account: mail.example.com, Server:
> ‘smtp.example.com’, Protocol: SMTP, Port: 587, Secure(SSL): Yes,
> Error Number: 0x800CCC0F
This mail account requires username and password in order to send mail. To protect against sniffing, I prefer to encrypt my authentication traffic in IMAP and SMTP. To narrow down the issue, I disabled SSL and found that I was able to send email successfully. Next I attempted to send a message with SSL while connected to a different network. This time I got a different error with a link to a Symantec Knowledgebase article.
“An encrypted email connection has been detected. Please see help for more information on how to transmit encrypted email.”
It turns out, that Symantec says:
If your Internet service provider uses the SSL in email protocol, you might have problems sending email messages. In this case, you might need to disable Symantec AntiVirus email scanning.
In order to be able to send email and use SMTP over SSL, I had to disable the Internet Email scanning within Symantec Antivirus. This is still secure because the file system real-time protection will still scan any file attachment. Message bodies will no longer be scanned, and the message will be scanned at attachment open/save rather than when the email message is open. For years Symantec didn’t even have a Internet Email scanner in their corporate product, so I don’t think disabling it is a huge risk.