While there may be any number of reasons for the failure, many ISPs and organizations block outbound network traffic on port 25 (the SMTP port) that mail servers use to communicate with each other as one method of stopping spam.  If you are using CS's server for your outgoing mail server, we recommend you use port 587 (the Submission port) with STARTTLS turned on.  For more information see our Email Configuration page. if you still encounter problems sending mail please do not hesitate to email help@cs.utexas.edu and we will try to help you resolve the problem.

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