FAQ Email

What is a mailbox quota and what happens when it is full?

What a mailbox quota is, what happens the moment a mailbox reaches it, and how to free up space again.

iFastHosting Support Team Updated 26 August 2026 4 min read Beginner

A mailbox quota is the amount of storage allowed for one specific email account, separate from the disk space allowance for your website or hosting account as a whole. Every message, and every attachment inside it, counts toward that account's quota until it is deleted.

What happens when a mailbox reaches its quota

Once a mailbox is full, new incoming mail is refused rather than queued or held for later delivery. The sender typically receives a bounce message stating the mailbox is full or over quota, and the mail is not retried automatically once space is freed — it is simply gone from the sender's side, and they would need to send it again.

A full mailbox does not queue mail for later

This surprises people who assume a bounced message means "it will arrive once I clear space" — it does not. Anything sent while the mailbox was full has to be resent by the original sender after space is freed, since the receiving server rejected it outright rather than holding it.

Checking how much space is used

The email section of your control panel shows current usage against the quota for each mailbox, usually as a simple figure or bar next to the account. Check this periodically for any mailbox that receives a high volume of mail or large attachments, rather than waiting for it to fail.

Freeing up space

Delete old messages you no longer need, particularly ones with large attachments, which usually account for a disproportionate share of the total.
Empty the Trash or Deleted Items folder. In many setups, deleted mail still counts toward the quota until this folder is emptied separately.
Empty the Sent folder of anything large you no longer need a copy of, since sent mail also counts toward the same quota.
Download attachments locally, then delete them from the message if the content matters but the storage does not need to live in the mailbox permanently.

IMAP and webmail both show the same usage

Because IMAP keeps mail on the server, deleting a message from any connected device or from webmail reduces the same quota — there is no need to delete it from every device separately.

Increasing the quota

Whether a mailbox's individual quota can be raised, and by how much, depends on your specific hosting plan's overall allowance and how it is divided between mailboxes in your control panel. Check the email section of your control panel for the option, or contact support if you need help working out the best way to allocate space across several mailboxes on one plan.

Preventing it happening again

For a mailbox that regularly approaches its limit, consider whether it needs to retain everything indefinitely, or whether periodically archiving older mail elsewhere — many mail clients support exporting messages to a local file — would keep it comfortably under quota without losing anything important.

If a mailbox has stopped receiving mail and you are not sure whether quota is the cause, fixing email you are not receiving covers this alongside the other common reasons, including DNS and spam filtering.