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Troubleshooting mail-delivery problems

If your email fails to reach its destination or bounces back, here are several things you can try to help diagnose the problem before calling the SCS HelpDesk.

Several useful tools for troubleshooting:

  • finger: See where an SCS user's e-mail is forwarded, for example: finger
    This command is available on Unix hosts and also via a Windows command shell. You can also finger people at other sites, although many do not accept such requests.
  • ping: Determine whether a host is "alive" and on the network, eg. ping
  • traceroute: Examine the network path between your machine and the host you are trying to reach, eg. traceroute Note: Windows calls this command tracert
CMU Computing Services offers a Web-based gateway to the ping and traceroute commands [offsite link, will open in a new window].
  • First, try sending another copy of your message to make sure the problem wasn't caused by low disk space or a temporary network problem
  • If a mail message is returned to you, the error message will often come from MAILER-DAEMON. Read the entire error message carefully. You will often find more detailed information than simply "undeliverable mail" if you sift through the text.
  • "Undeliverable mail" or "bad host name" errors: Verify the intended recipient's address using the finger command or another means. You can use ping to see if the host is reachable. Note: In certain situations, the host part of a valid e-mail address may not be pingable and will not resolve to an IP address. However, the DNS MX (Mail Exchanger) record for that host will list servers that should be pingable. Use the hostq command on a Facilitized Unix host to examine MX record for a particular hostname.
  • Local configuration errors: finger the intended recipient to see if there is another account to which you can send e-mail. These problems can usually only be handled by the recipient's local mail administrator. Try sending mail to "postmaster" at that address.
  • Looping message errors: This usually happens because of a forwarding loop (two different mail systems forward mail to each other). These problems can usually only be handled by the recipient's local mail administrator. Try sending mail to "postmaster" at that address.
  • System timeout during mail transfer errors: This is usually caused by a system or network-load problem. You can use ping to determine whether the remote host is currently reachable and traceroute to examine the connection path between here and there.
  • Temporary errors: you may occasionally get an error indicating the recipient is over-quota or that your mail encountered temporary problems on the remote site. First, confirm that the bounce message is really a notification of delivery failure and not merely a warning that your message is waiting in a mail queue. Normally, mail systems will automatically retry messages when a temporary failure occurs. If not, try resending your message.
  • Messages rejected as SPAM or because of a blacklist: At times, our outgoing mail servers may get listed on one of several blacklist sites, causing another (non-CMU) site to reject mail from us. Please refer such cases to SCS Computing Facilities so that we can request removal from the blacklist. Forward the bounced message in its entirety (including all headers), so that we can determine which blacklist is affecting us.