Email Troubleshooting Mailbox Size


Having an over-full inbox can cause a variety of email problems, including slow performance, timeouts, connection problems, and disk quota errors. Follow this article to diagnose and resolve mailbox disk space issues.


Email takes a very long time to send or receive, email takes a long time to connect, or doesn't load at all.

Likely cause: You have a very large amount of email stored in your mail account.

Solution: Remove or archive some email. See Reducing Mailbox Size below.

Disk Quota Exceeded error received.

Cause: You have exceeded the disk space either for this specific mail account, or for the domain as a whole.

Solution: You must delete some content from your server/domain/mailbox. Mailboxes are limited and each has a subscription quota.

Reducing mailbox size

The ideal size for a mailbox is 50 MB or less. However, many users will be very content with email performance up until about 500 MB or so. At that point, or for accounts with greater than 500 MB of email, you should seriously consider removing or archiving some of the emails. Otherwise, you will notice degraded performance for that mail account.

  1. Diagnose that mailbox size is what is causing your problem.
    • Review your disk or mailbox usage.  Which users or folders are taking up the most space.
  2. Next, you need to access your email account. The best way to do this is to set up an IMAP connectionto the account with your favorite email client software.
  3. Then, delete and archive unneeded emails.


    Many email programs will let you create local folders that are stored on your computer, rather than on the server. You can drag and drop messages from your inbox or Sent folder on the server to your local folder instead. Then, if you ever need to reply to or forward them, just drag them back to your inbox. Note that you should consider having a backup option for your local computer if you do this, because the messages won't be on the server.

  4. If you can't get into your email account with IMAP, you have two options:


    The next option will delete all or some of your email, with no regard for individual messages. Pursue these options at your own risk.

    • Try to set up a POP account instead of IMAP. Make sure it is configured to download your email and NOT leave a copy on the server. Note that all of your email will now be on the machine you used for downloading, and not on the server.
    • Remove and then recreate the account on the server. You'll need to wait about twenty minutes after removing the account before you recreate it. This will delete all messages from all folders on the server.
  5. Try to get your mailbox size down to 50 MB or less. Note that lots of small files are more likely to slow down your email than a few large attachments.
  6. When you're done, see if your email responds more quickly and/or stops giving you errors.