A "mailbox full" error means your email account has reached its storage quota. When this happens, incoming messages bounce back to the sender with a delivery failure notice. The fix is straightforward: free up space in your mailbox and, if necessary, increase your quota or upgrade your hosting plan. Follow the steps below to resolve this quickly.
Mailbox limits by plan
Before you start troubleshooting, check which plan you are on — your mailbox storage limit depends on it:
| Hosting Plan | Mailbox Size Limit |
|---|---|
| Personal Shared Hosting | Up to 1 GB per mailbox |
| Business Shared Hosting | Unlimited mailbox size |
Step-by-step fix
Work through these steps in order. Most mailbox full issues are resolved within the first three steps.
Log in to your hosting control panel at yourdomain.com:2083 and navigate to Email Accounts. You will see a usage bar next to each email account showing how much storage is currently in use and what the quota is set to.
If the usage shows 100% or close to it, your mailbox is full and you need to free up space.
Log in to webmail at yourdomain.com:2096 (or webmail.yourdomain.com) and start by removing emails you no longer need. Focus on these folders first, as they tend to consume the most space:
- Spam/Junk — these accumulate quickly and are rarely needed
- Trash — deleted emails still count toward your quota until the Trash is emptied
- Sent Items — emails with large attachments that you sent can take up significant space
- Inbox — sort by size to find and remove the largest messages first
After deleting emails, they move to the Trash folder — they are not actually removed until you empty it. In Roundcube:
- Right-click the Trash folder in the left sidebar
- Select Empty to permanently delete all messages in it
- Repeat for the Spam (or Junk) folder
If you want to keep old emails but free up server space, download them to your computer using an email client configured with POP3:
- Set up your email client (e.g., Outlook, Thunderbird) using POP3 with port
995(SSL/TLS) - In the POP3 settings, enable the option to delete emails from the server after downloading
- Download all emails — they will be saved locally on your computer and removed from the server
If your plan allows it, you can increase the storage quota for your email account:
- Log in to your hosting control panel at
yourdomain.com:2083 - Go to Email Accounts
- Click Manage next to the affected email account
- Under Allocated Storage Space, increase the quota value
- Click Save
Keep in mind that the total mailbox storage is limited by your hosting plan's overall disk space allocation.
If you consistently run out of mailbox space and the steps above only provide temporary relief, it may be time to upgrade:
- Business Shared Hosting plans offer unlimited mailbox size, making mailbox full errors a thing of the past
- Business plans also include higher sending limits (1,000 emails/hour vs. 100 on Personal plans)
You can upgrade your plan through the HOSTDOG Client Area.
Prevent future mailbox full errors
Once you have freed up space, take these steps to avoid running into the same problem again:
- Set up POP3 to delete server copies — if you use an email client, configure it with POP3 and enable the option to remove messages from the server after downloading. This keeps your server mailbox lean while retaining all emails locally.
- Regularly clean up Spam and Trash — make it a habit to empty these folders weekly.
- Avoid sending large attachments via email — use cloud storage services and share links instead of attaching large files.
- Set up email filters — automatically move newsletters and non-essential emails to specific folders, making it easier to delete them in bulk.
Frequently asked questions
Yes. When your mailbox is full, the mail server rejects incoming messages and sends a bounce-back notification to the sender. Those emails are not queued or stored — they are returned. Once you free up space, ask the senders to resend any important messages.
Deleted emails are moved to the Trash folder, which still counts toward your quota. You must empty the Trash folder to actually free up the space. Also check the Spam/Junk folder, as it may contain a large number of messages taking up storage.
IMAP keeps emails on the server and syncs them across all your devices. This is convenient but means your server mailbox grows over time. POP3 downloads emails to your device and can be configured to delete them from the server, freeing up space. If storage is a recurring issue, consider using POP3 or setting your IMAP client to only sync recent emails.
You can increase the quota for individual mailboxes through your hosting control panel, as long as you have not exceeded your plan's total disk space. If your overall disk space is also full, you will need to free up space on the hosting account (files, databases, other mailboxes) or upgrade to a plan with more storage.
In your email client's account settings, look for a POP3 option labelled "Delete from server after download" or "Remove messages from server". In Outlook, this is under Account Settings > More Settings > Advanced. In Thunderbird, go to Account Settings > Server Settings and check "Leave messages on server" to uncheck it, or set a retention period (e.g., delete after 14 days).