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Quotas and the SCS IMAP Server

Note: This document describes the implementation of mail quotas on the SCS IMAP Server

SCS Facilities provides an IMAP server, imap.srv.cs.cmu.edu, for use by the SCS community. To take full advantage of the IMAP server, users are encouraged to store all of their e-mail messages on the server, which allows them to access their mail from any IMAP client. As with any shared resource, unfortuantely, comes the possiblity that a particular user may (either intentionally or unintentionally) impact other users of the service. In the case of the IMAP server, one user may receive enough mail to cause a disk partition to fill up, which would prevent all users on that disk partition from receiving their e-mail.

In order to prevent this from happening, SCS Computing Facilities is implementing a quota system on our IMAP e-mail servers which will limit the amount of disk space any particular user may take up. This document outlines how the IMAP quota system is implemented, how users may recognize when they are near or over their quota, and how to remedy this situation.

    Quota Implementation

    A disk quota limits the amount of mail that you can store on the IMAP server. IMAP quotas are different from (and do not count towards) your AFS disk quota, or any quota that may exist on another UNIX system you may log into. During the planning for the IMAP server architecture, the disk arrays and partitions were sized to allow for fifty users per partition, each using a maximum of two gigabytes of storage each. Therefore, the normal quota for IMAP users is two gigabytes per user.

    Am I subject to the quota?

    If you have your mail sent to the IMAP server (that is, your mail is forwarded to either the host "imap.srv.cs.cmu.edu" or "imap-ns.srv.cs.cmu.edu (deprecated)", then you are subject to the quota. It is important to note, howver, that your mail may not be stored on the server. If you use an IMAP client (such as Outlook, Mozilla, or the webmail client) then your mail is most likely stored on the IMAP server. If you use a POP client (such as MH, Pine, or Thunderbird) that downloads your mail to your local system, then your mail may not be stored on the server, and you may not be affected by the quota. If you are unsure, contact SCS Computing Facilities (help@cs.cmu.edu) for assistance.

    Another possibility is that your mail is being sent to the Microsoft Exchange server that is maintained by SCS Computing Facilities. This is the case if you mail is being forwarded to "exchange.cs.cmu.edu". In this case, you should review the following document, which describes the quota system implemented on the Exchange server.

    Note that if you are currently receiving your mail on one of the "UX" machines (ux1 through ux15) you are not affected by the IMAP mail quota system. Since these machines have many individual users receiving mail there, though, you may encounter times when the mail spool partitions fill up and you are unable to receive new mail. SCS Computing Facilities is in the process of planning the retirement of the UX mail servers, and strongly encourages those users to migrate to the IMAP mail system. Contact SCS Computing Facilities (help@cs.cmu.edu) for assistance in moving to the IMAP server.

    What if I need more than 2 gigabytes of space?

    It is important to note that the e-mail quotas are not intended to limit the amount of legitimate mail that you store on the IMAP server - quotas are designed to limit the impact that a single user can have on other users. If you currently have more than two gigabytes of e-mail stored on the IMAP server, or think you will need more than the normal quota in the near future, you are encouraged to contact SCS Computing Facilities (help@cs.cmu.edu) for an increase in your quota.

    Recognizing when you are near or over quota

    The IMAP server enforces two different quotas for user e-mail:
    • a "soft" quota, reached at 95% of your listed quota (normally 2 gigabytes per user). When this quota is reached, you will begin receiving notification that you are near your quota. When you reach your soft quota, you can still receive new mail into your IMAP mailbox.
    • a "hard" quota, which is normally 2 gigabytes. When this quota is reached, you will not receive any new mail into your IMAP mailbox until you reduce your disk usage below your quota.
    When you reach your "soft" quota, the IMAP server will begin informing your e-mail client that your mailbox is near its quota. How your e-mail client displays this warning depends on the particular client you are using. Some common clients are listed below, along with how they notify users.

    Webmail Interface

    Currently, the SCS webmail client (reached at https://webmail.cs.cmu.edu), does not display quota warning messages. SCS Computing Facilities is attempting to implement this feature.

    Netscape/Mozilla/Thunderbird

    These related e-mail clients will display the quota warning in a small pop-up box, as seen below.

    mozilla quota display

    Microsoft Outlook

    Microsoft Outlook displays the quota warning in a small pop-up box, as seen below.

    outlook quota display

    Eudora

    Eudora mail clients older than version 6.0 do not display any quota warning messages from the IMAP server. Eudora version 6.0 and newer do display the warning message in the status box near the bottom of the client window.

    The warning message will be:

    Warning,The IMAP server has issued the following alert [11:50:39AM]
    [ALERT] Mailbox over quota


    Evolution

    The version of Evolution installed on the facilities RedHat 9 Linux does not display quota warnings.

    Pine

    Pine will display the warning message in the "status" area at the bottom of the screen.

    MH/exMH

    MH and exMH do not use the IMAP protocol to retrieve the mail from the server, and therefore do not display any warning messages from the IMAP server.

    Remedying the Over-Quota Condition

    In order to fix the over-quota condition, you should remove mail from the IMAP server. To do this, you have several options:

    • Empty your trash folder. Most e-mail clients have a "trash" folder where deleted e-mail messages are stored. You should be able to empty this folder through your e-mail clients interface. For example, under Netscape/Mozilla, you can select the "Empty Trash" item under the "File" menu. You should review the contents of your trash folder to make sure that there are no messages that you want to keep.
    • Compact  your folders. In some cases, when you delete an e-mail message, it is not moved to the "trash" folder, but is simply marked as being deleted. In this case, the message is still on the server until you "compact" your folders. You can compact your folders through your e-mail client interface. For example, in Netscape/Mozilla, you can select "Compact Folders" from the "File" menu.
    • Delete SPAM messages. If you are set up to use the anti-SPAM service, messages that are identified as SPAM are refiled automatically into a folder under your INBOX. This folder is often named "SPAM" or "Junk". You should review the contents of these folders periodically and delete messages that are clearly SPAM.
    • Delete messages you no longer need, especially from your "Sent" folder. Most e-mail clients automatically file a copy of outgoing messages under the "Sent" folder. You should review the contents of this folder periodically to weed out messages that you do not need.
    In deleting messages, you should pay special attention to messages that may have large attachments. These can take up a large amount of disk storage on the IMAP server - if you do not need the message (and attachment) any more, you should delete these messages if possible.