Management of Received E-mail on Central Service Hosts

Audience:

All University users of central NUIT e-mail servers

Definition:

The central e-mail servers (lulu, hecky, merle, and casbah) provide service to over 20,000 University NetID holders. These service hosts must operate as efficiently as possible. An important aspect of performance is disk space use. The servers will be operated with consistent limits of 100MB for pending e-mail messages within individual accounts. As accounts approach the 100MB limit, a series of warning messages will be sent prior to archiving the pending e-mail. Accounts that reach 200MB in pending message space will no longer receive messages until the space is reduced or the pending messages are archived.

Policy Statement:

Archived messages can be restored from backup storage for a period of 120 days. (Please send an e-mail message to email-accounts@northwestern.edu to request this service).

This formula for disk storage management is a liberalization of past procedures that allowed for less storage and that had no hard ceiling at 200MB.

Glossary of Terms

Archiving of messages

The removal of pending messages from a UNIX account inspool to backup storage.

Inspool

A UNIX system file that holds all pending e-mail messages received for an account.

Pending e-mail messages

Messages for an account that have not been read or have been read but neither moved to another computer, nor moved to a storage folder on the server.

Restoring messages

Copying archived messages from backup storage into the account inspool to make them available for processing by the account holder.

Standards

Inspool-resident e-mail messages (pending messages) will be subject to disk space quotas as follows:

• Less than 60MB of storage used. Normal operations. No special notices or actions.

• Between 60MB and 80MB of storage used. Weekly warning messages are sent to the account asking that the NetID holder remove pending messages.

• Between 80MB and 100MB of storage used. Daily warning messages are sent to the account reminding the NetID holder that

  1. large messages or large numbers of messages affect e-mail service performance, and

  2. the account is approaching the 100MB limit on inspool size.

• Between 100MB and 200MB of storage used. A daily message is sent indicating that the account is over quota and referring to a Web page explanation of this policy and process. If the account inspool remains over 100MB for 10 days, then the account is marked as EXPIRED - new e-mail then begins bouncing as undeliverable. An alert message is forced into the inspool indicating that e-mail is being rejected. After one additional day, the entire inspool is archived. At this point the account would be at 0 MB and can to receive e-mail again.

• At 200MB of storage used. No additional messages are accepted and bounced messages indicate that the account cannot receive e-mail. An alert message is forced into the inspool indicating that e-mail is being rejected. After one additional day of being over 200MB, the entire "inspool" is archived. At this point the account would be at 0 MB and can receive e-mail again.

When pending messages are moved to secondary storage, all messages are moved. It is not possible to separate read versus unread messages during this process, nor is it possible to move only the oldest messages. If the user does not take action to avoid this process, then unread messages received very recently could be moved to secondary storage.

There is no charge to restore "inspool" from secondary storage. Faculty and staff requests are handled promptly, within two business days. An online form is available for restoral requests.

In addition to the 100MB inspool quota, IMAP users are allocated a maximum 100MB of server space for storage of mail folders. Faculty can purchase an additional 300MB of server folder space for $5.00 per month. This can be purchased on a month by month basis and turned on and off as required. For additional information on this process, please see the Additional IMAP Folder Space for Faculty Web page.

Restoration is not selective -- all archived e-mail will be restored and appended to the "inspool" for that account. This will likely put the account into an immediate over quota condition, which the user must deal with quickly. The archived messages, regardless of whether they have been read or not read, will be retained for 120 days and then discarded.

Background Issues:

Disk storage on the central e-mail servers is an important resource. Overall server performance, cost of operations and equipment, and performance of individual accounts are all influenced by disk storage. For the past few years, NUIT has had informal procedures for protecting e-mail service through warning messages and the removal of e-mail to secondary storage. These procedures have varied from server to server based upon the hardware storage available and the number of accounts. The effective amount of storage has varied between 6MB and 40MB in this unpublished approach.

E-mail use has grown tremendously, making performance of the central servers a vital concern for academic, research, and business continuity. NUIT has invested in a series of server upgrades and now looks to optimize these resources for e-mail delivery. In parallel, new e-mail access methods are to be deployed to address the needs of mobile users (IMAP).

By announcing a policy on received e-mail storage quotas, NUIT will create a more predictable service environment. The change is itself an improvement of service to the NetID holder, since more space is being allotted under the new processes. The notification process will be more graceful and will allow more time to cure quota violatons. The compromise is that very large queues of received messages will eventually result is new messages being returned to the sender as undeliverable.

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