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Managing IMAP mailboxes

  knowledgebase  :: network status

IMAP allows storage of email on the server ("in the cloud"), and can consequently offer the ability to "sync" mail between devices. However, mailboxes on the server have a finite capacity (quota). Therefore, management of an IMAP mailbox is necessary, to avoid filling the mailbox. If your mailbox fills, you will no longer be able to receive email, and people who email you will get a "bounce" message telling them that your mailbox is over-quota.

Note: If your account is already over-quota, to get it working again right now, all you need to do is delete some large, unwanted messages (and then purge your deleted items). This will free up space in the mailbox and will hopefully bring you under quota. You should also check your auto-archiving settings (see notes below).

While it is possible to increase the quota, to a certain extent, this will only defer the problem, not solve it. Long-term, the only solutions are to either use POP3 instead of IMAP, or ensure to manage your mailbox, such that it stays under quota.

We recommend using an offline storage area to archive your mail. This storage area will be displayed by your mail software as "local folders", "personal folders", "archive folders" or similar. As it's located on your computer, not the server, the capacity of your offline storage area is limited only by the size of your hard drive. However, once a mail is moved to offline storage, it will no longer be visible on any of your other devices.

Below are some points to consider when managing your IMAP mailbox:

  1. Deleting a mail from an IMAP mailbox does NOT actually delete it. If deleting mail to free up quota, ensure to purge deleted mails, otherwise no quota will be freed. The procedure to purge deleted mails varies from program to program, and is not detailed here. If your mailbox says it's full, when it seems empty or near-empty, ensure to purge your deleted mails.

  2. If deleting mail to free up quota, ensure to delete mails from "subscribed" (IMAP) folders only. There is no need to delete mail from other folders - it's only the IMAP folders which count against quota. Try not to delete mail though - just move it to your offline storage area (see next point).

  3. Regularly move old, unnecessary, large messages to your offline storage area. Or, just configure auto-archiving (see next point).

  4. Ensure your mail program is configured to auto-archive old mail. This is recommended as it means you don't need to remember to do it manually. Auto-archive stores your old mail in your offline storage area, not on the server, freeing up space on the server for new mail. Popular mail programs, including Outlook and newer versions of Apple Mail, include an auto-archive feature. Auto-archive support can be added to Thunderbird using extensions such as AutoarchiveReloaded and Awesome Auto Archive.

  5. Keep an eye out for quota warnings from your hosting provider. You will be emailed warnings when your account is approaching quota (not all providers offer this, however).

  6. Keep an eye on the current total mailbox size. On Windows, we recommend using IMAPsize for this. IMAPsize is purpose-built for checking total mailbox size, folder sizes, and total quota, and can be used alongside Outlook, Thunderbird etc. It also has a very flexible search function, and includes various other tools. On OSX, Apple Mail can display a listing of IMAP folders and their sizes (in a format similar to IMAPsize).

    Thunderbird, IMAPsize and Apple Mail include a feature to check total mailbox size and available space, however it requires that the server supports RFC 2087.

Note that unless you need to use IMAP's sync feature, you're probably better off using POP3. However, the pros and cons of each protocol are not currently covered here.

See also: