When a mailbox reaches its storage limit (its quota), new mail sent to it bounces back to the sender with a "mailbox full" or "quota exceeded" error, and you may not be able to send either, because your email program can't save a copy to Sent. The quick fix is to empty Trash and Junk and delete or archive the largest messages. The lasting fix is to understand what is filling the mailbox, set up an archive for old mail and give busy mailboxes a size that fits how they are used.
How to tell that a mailbox is full
- Customers tell you their emails to you bounced, with a message mentioning quota, storage or "mailbox full".
- Your email program shows an error when sending, or messages stay in the Outbox.
- Webmail shows a storage bar close to 100%.
- Mail seems to "stop arriving" with no other explanation.
The bounce is the costly part. A customer whose order or quote request bounces may simply try a competitor, and you will never know.
What fills a mailbox
It is rarely the number of emails. It is the size of a few of them.
| What | Why it adds up |
|---|---|
| Attachments | Photos, scanned documents, PDFs and presentations, often received several times in a thread |
| Sent items | Every attachment you send is stored again in Sent |
| Trash and Junk | Deleted mail still counts until the folder is emptied |
| Forwarded copies | A mailbox that keeps a copy of everything it forwards stores it twice |
| Old shared addresses | info@ or accounts@ mailboxes that years of mail flow into and nobody cleans |
IMAP, POP3 and storage
With IMAP, mail stays on the server and syncs to every device, so the server mailbox holds everything. With POP3, mail is usually downloaded to one computer and deleted from the server, which saves server space but leaves only one copy, on one device. IMAP is the better choice for most businesses; just plan for the storage. See IMAP vs POP3 for the full comparison.
Free up space now
Work through these in order and check the storage bar after each:
- Empty Trash and Junk. In webmail and in your email program, as both may keep their own copies.
- Find the largest messages. In webmail or Outlook, sort or search by size and look at everything over a few megabytes. Save attachments you need to your document storage, then delete the email or remove the attachment.
- Clean Sent items. Sort Sent by size too. Large attachments you sent are usually saved elsewhere already.
- Delete old newsletters and notifications. Search by sender and delete in bulk.
- Check other folders. Old project folders and subfolders created by rules are easy to forget.
Archive instead of hoarding
Many people keep everything in the mailbox because they're afraid of losing something. An archive gives you a place to put old mail that is still searchable but doesn't count against the server quota.
- Outlook can move old mail to a local archive file on the computer.
- Thunderbird and Apple Mail can move mail into local folders that are stored on the computer only.
A local archive is only as safe as the computer it is on. Include it in your backups, or you have simply moved the risk. Our guide to a website backup strategy that works uses the same 3-2-1 idea: three copies, on two kinds of storage, one of them off-site.
A simple routine
Once a quarter, archive mail older than a year from busy mailboxes, empty Trash and Junk, and check the storage bars. Put it in the same calendar reminder as your other admin.
Give the mailbox the right size
Some mailboxes genuinely need more space: a director who receives large drawings, an accounts mailbox full of statements, a shared info@ that the whole team works from. Increasing the quota is often cheaper than the time spent cleaning every month.
On NewHost email hosting, each mailbox has its own size. You set it when you create the mailbox and can change it later in the mailbox's Settings in the dashboard, within your plan's limits. If you need more total space than your plan allows, compare the email plans on the pricing page or ask us for a quote.
Use aliases instead of extra mailboxes
If sales@ and info@ are read by the same person, they don't need separate mailboxes that each fill up. Make one of them an alias that delivers into the other mailbox. Our guide to forwarders, aliases and shared mailboxes explains which to use when.
Retention and POPIA
Keeping every email forever is not just a storage problem. Mailboxes are full of personal information: names, phone numbers, ID numbers on application forms, medical notes, bank details. POPIA section 14 says records of personal information should not be kept longer than necessary for the purpose they were collected for, unless a law or contract requires you to keep them longer.
A practical approach:
- Decide how long different kinds of mail must be kept. Your accountant can tell you what financial records you need to retain.
- Delete or archive mail that is past that period, especially attachments containing personal information.
- Keep archives protected: an archive file on an unencrypted laptop is a risk if the laptop is stolen.
For your specific obligations, take professional advice. Our guide to POPIA-compliant hosting covers the hosting side.
Frequently asked questions
Do bounced emails get delivered once I free up space?
No. A bounced message was returned to the sender and isn't queued for you. Ask anyone whose mail bounced to send it again.
Does deleting mail on my phone free space on the server?
With IMAP, yes, once the deleted mail is also removed from Trash. With POP3, deleting on the phone usually doesn't affect the server copy.
Is it safe to delete attachments but keep the email?
Yes, if you have saved the attachment somewhere else that is backed up. Outlook and some other programs can remove an attachment from a message while keeping the text.
How big should a mailbox be?
It depends on how the mailbox is used. Most people's mailboxes are filled by attachments, so look at who receives large files and size those mailboxes more generously.
Running out of space on your current email? NewHost email hosting lets you set each mailbox's size in the dashboard, with webmail and IMAP on your own domain.