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Mail Service Policy Rules: Constraints and Features

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Use of the CERN Mail Services are covered by the CERN Computing Rules, operational circular no 5 and the subsidiary rules for use of e-mail services.

In order to protect the services from abuse, the following size constraints are also enforced.  

  • Message size limits

    Since excessively large messages can affect performance of electronic mail, there is a general limitation on the size of all the mail messages exchanged within CERN which is fixed at 50 MB.
    Messages with a size greater than 50 MB will not be delivered; the sender will receive a notification explaining that the message was refused.
    Note that this limit applies to electronic messages exchanged between CERN users. When a large e-mail is sent to people outside CERN, the recipient's organization may refuse the large message; the maximum size of a message sent to a person outside CERN depends on the policy defined by the recipient's own organization. When sending e-mail to people outside CERN, it is recommended not to exceed 10 MB, as many organizations are likely to refuse larger messages.

  • Folder storage limit on the Mail Servers

    The default quota for electronic mailboxes hosted on the CERN Mail Services is set to 2GB, and can be extended at user's request.
    A warning message is issued when the limit is reached or about to be reached. If users cannot free some space by deleting old mails they no longer need, they can request their quota to be increased. For more information see What to do when running out of quota.  

  • Limit on number of e-mail addresses that can be addressed by a single user per period of 24 hours

Starting from June 8th, 2011 the number of e-mail addresses that a CERN e-mail user can address will be limited to 3000 per period of 24 hours. This limit is meant to limit the potential damages that compromised CERN accounts could inflict on other CERN users

A message sent to an e-group with many members is counted as 1 e-mail address, regardless of the number of members in the e-group. In case a CERN user needs to address more than 3000 e-mail addresses in a single day, it is recommended to create an e-group to combine the many e-mail addresses ( If ever the limit is reached and a user tries to send new messages, an error stating that the user has reached the submission quota will be returned until the next day. In this case, it is still possible to contact the service desk by phone or the web portal in order to reset the quota.

NB: this policy applies to messages send by human users using e-mail clients (webmail, Outlook, Thunderbird, Alpine, Mac Mail etc.). It does not affect automatic messages sent by scripts, applications or cron jobs, as long as they are configured according to the recommended instructions in