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Outbound mail filter

Aim: Explanation of how email leaving the Nikhef mail server is filtered and handled.

Outbound (sender) filtering

The outbound (sender) mailfilter provides rate limiting and filtering on outbound email sent through the Nikhef mail servers to the outside world. This should prevent the unfortunate situation where the Nikhef mail servers are 'blacklisted' by major email providers because of sending massive spam by (potentially hacked) Nikhef accounts. Outbound mail filtering is done by the (external) SURFmailfilter. The filtering involves several measures:

  • The maximum number of messages per sender is limited to 500 recipients per hour, regardless of where you send them from;
  • All mail destined outside of Nikhef is scanned for viruses and spam;
  • When you use the Nikhef mail servers outside Nikhef (i.e. on the road or from home) be sure your sender (from) address is one of your valid Nikhef email addresses (see below).

Note: no sender validation is performed in case you send the mail from inside the Nikhef network. Mail sent through Nikhef mail servers to internal addresses is not filtered and always remains inside Nikhef.

Blocked mails

In case the mail servers refuse to deliver your message, you will be notified by an email with the reason. If you think the block is in error, or if you have specific email needs, please contact the CT helpdesk to arrange for a time-limited exception.

Nikhef email address

Valid Nikhef email addresses are:

  • the sender@address is the name or an alias of your personal mailbox at Nikhef, e.g.,,;
  • the sender@address is your registered preferred email contact address (the one where you receive account notices, which may be at CERN, at your home university, or even at home);
  • the sender@address is the email address of a group list that you are a member of, or of which you are the owner (e.g. the user davidg can send mail pretending to be;
  • the sender@address has been added as an exceptional permission to your computer account entry.


The SURFmailfilter checks all incoming and outgoing mail for the domain, and all other domains which we are hosting.