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Guidelines for Administrators of
Penn E-mail Systems

On a campus with over 30,000 e-mail accounts like Penn, it is important to consider the impact of e-mail on the total computing environment. Mail messages affect computer systems and networks in ways that message senders often cannot control and rarely consider.

Administrators of large e-mail systems, by following the guidelines below, can help reduce the unpredictable nature of e-mail on the electronic environment. The guidelines should be understood in the context of Penn's Policy on Acceptable use of Electronic Resources and current e-mail policy.

Maximum Size of Messages

Guideline To minimize potential service disruptions, all campus e-mail servers should be configured to restrict the size of outgoing mail messages to a maximum of 20MB. In addition, e-mail servers should be configured to reject incoming messages that exceed this threshold.

Notes Each recipient of a message usually receives a copy of the message in a shared incoming mail area called the spool area. A large message sent to only a few people can fill the shared spool area and prevent additional e-mail from being received by users on that host. The resulting denial of service to users can be caused inadvertently or maliciously by the sender of a message.

Management of Mail Spool Area

Guideline To facilitate the management of individual users' e-mail environments, all campus e-mail servers should be configured to exclude incoming mail from a user's total disk quota, to limit spool areas to no more than 20MB, and to issue warnings when spool storage exceeds 500KB for an individual user.

Notes When individual disk quota's are enabled, it is possible to configure the user's total quota to include or exclude the incoming mail spool.
  • If the server is configured to include the spool area in the user's total quota, incoming mail will be rejected if new messages are sent that exceed the quota, and individual users will be locked out of their accounts and unable to make space available without intervention by a system administrator.

  • If the server is configured to exclude the spool area from the user's total quota, limits are usually set on the size of an individual's spool area and warnings are typically sent to users when their incoming mail exceeds a pre-defined threshold. In this case, users have the opportunity to make space available so that mail is removed from the spool area.

    The down side to this configuration is a greater possibility that a user will receive e-mail that disproportionately occupies the shared incoming spool area and is unfair to other users. To make matters worse, some users configure their POP e-mail clients to leave messages on the server, further filling the shared spool area with additional messages that are already read. Setting a relatively low threshold for warnings mitigates this problem at the expense of being a nuisance to the user.

Use of e-mail clients that download incoming mail to desktop computers (via POP mail, e.g. Eudora) helps to reduce the pressure for more server disk storage. However, creation of web home pages, as well as IMAP-based mail (likely to become popular over the coming year) will increase the pressure for more server storage space.

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