Email Quota Full or “Mailbox Over Size Limit” Fix

Your mailbox has a storage limit. When it fills up, incoming mail bounces with a “mailbox over size limit” error and senders see an immediate failure notice. The good news: there are three independent fixes — cleaning up, archiving, and increasing the quota. This guide covers all three, plus how to set things up so you don’t run into the wall again.

Check your current usage

In cPanel: Email → Email Accounts. Each mailbox shows its disk usage and quota. Sort by usage to find the biggest offenders.

In DirectAdmin: E-mail Manager → E-mail Accounts. Same data, slightly different layout.

You’ll often find one mailbox using 80%+ of the space and the others nearly empty — usually info@ or support@, where everything funnels.

Option 1 — Clean up

Delete what you don’t need. The biggest space wins, in order:

Spam folder

The first place to look. Spam folders quietly accumulate gigabytes of junk most people forget about. In your mail client or webmail:

1. Open Spam (or “Junk”, depending on the client).
2. Select all messages.
3. Delete permanently — not “move to trash” but actual permanent delete.

This alone often frees 30-50% of mailbox space.

Trash / Deleted Items

“Deleting” a message in most clients moves it to Trash — still occupying space. Empty Trash to actually reclaim disk:

• Webmail (Roundcube): right-click Trash folder → Empty.
• iPhone Mail: open Trash → Edit → Select All → Delete.
• Outlook: right-click Deleted Items → Empty Folder.

Large attachments

One forgotten 50 MB PDF accounts for a lot. In webmail, sort by size (Roundcube → Folder view → Sort by Size). Delete what you don’t need, save attachments locally first if you might want them later.

Sent folder

Often overlooked. Every email you’ve sent — and especially every one with an attachment — sits here too. Same cleanup approach.

Option 2 — Archive locally

If you can’t bring yourself to permanently delete old mail (legal/tax/sentimental reasons), download it to your computer first, then delete from the server.

Using Thunderbird (free, recommended)

1. Install Thunderbird from thunderbird.net.
2. Add your iWebVault email account (Thunderbird auto-detects IMAP).
3. Install the ImportExportTools NG extension.
4. Right-click any folder → ImportExportTools NG → Export folder. Choose .mbox format — standard archive format readable by any mail client later.
5. Save to your computer. Verify the export opens correctly.
6. Now safely delete the messages from the server.

Using cPanel’s webmail download

Webmail (Roundcube) supports per-message download as .eml files. Useful for archiving small numbers of messages. For bulk archival, Thunderbird is faster.

Option 3 — Increase the mailbox quota

If cleanup isn’t viable or you simply need more space:

1. cPanel → Email Accounts.
2. Find the mailbox → Manage.
3. Scroll to Storage Space. Increase from current value to a higher number.
4. Save changes.

Increase is limited by your overall hosting account’s disk quota — if your plan has 50 GB total and your mailboxes alone need 60, you’ll need to upgrade the plan instead of just the mailbox. See choosing the right plan.

DirectAdmin: E-mail Accounts → click the mailbox → change Quota → Save.

Preventing the issue in future

• Set the mailbox quota high enough at creation. 5 GB is a sensible default for most personal addresses; 10-20 GB for heavily-used customer-facing ones.
• Use IMAP correctly. Set your mail client to NOT keep a permanent local copy of every message. Most clients sync visible folders and archive on the server.
• Set up auto-archive rules. Outlook can auto-archive mail older than N months. Webmail can do this via filters.
• Enable email forwarding instead of multiple mailboxes where appropriate. If billing@, info@, and contact@ all funnel into the same person, three forwarders to one mailbox is more efficient than three separate mailboxes.
• Monitor quotas monthly. 5-second glance at the Email Accounts list catches problems before they bite.

Common mailbox issues

“I deleted thousands of messages but quota usage didn’t drop.” Some clients don’t actually flush IMAP delete operations until “Expunge” is called. In Roundcube: Folder view → Empty Deleted. In Thunderbird: right-click folder → Compact. Then quota updates.

“Senders get bounce-back errors but my mailbox isn’t actually full.” Sometimes the quota cache hasn’t refreshed. Try sending yourself a message; if that delivers, the issue is at the sender’s side. If it bounces, check both the per-mailbox quota AND the overall account disk quota — either being at limit blocks new mail.

“My account disk quota is full but mail is only 2 GB of it.” The disk is shared with files, databases, backups, logs. Use cPanel’s Disk Usage tool to see what else is eating space. Often it’s old backups in ~/backups/ or ~/jetbackup_backups/.

“Spam filter is over-filtering and I can’t find legitimate emails.” Train it. In Roundcube, mark false-spam as “Not Spam” — over weeks this calibrates the filter. Or relax SpamAssassin thresholds in cPanel → Spam Filters.

What’s next

• Setting up new accounts more sensibly? Setting up email in cPanel.
• Mail going to spam folders? Deliverability guide.
• Configuring across multiple devices? Setup guide for devices.

30 minutes of mailbox hygiene now prevents the “everything is broken” panic of a full mailbox in six months. Add it to your annual checklist alongside renewing the domain.