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MailBox quota exceeded email error – Top 5 causes, and how to fix it provides Outsourced Hosting Support to Web hosts and other hosting providers. Part of our services involve resolving technical support queries posted by hosting users.

A common support query posted by end users is – Emails bouncing with the error “550 MailBox quota exceeded“.

We’ll get to how we resolve this error in a moment, but first let’s see what IS this error.


What is email error “550 MailBox quota exceeded”?

Every hosting account comes with a space limit (aka Quota), like 500 MB, 2 GB, etc.

Hosting users can store files, databases or mails in this account as long as the total usage remains within that space limit.

On top of this, each mail account also has its individual space limit (say 100 MB).

If either the Hosting Account space limit, or the Email Account space limit is exceeded, no more files can be stored in the account.

So, any new file uploads or incoming mail will fail with a “Quota exceeded” error.

For emails, this error is “550 MailBox quota exceeded“.

Friends and business contacts trying to mail to the hosting user will a bounce with this error.


What are the reasons for “MailBox quota exceeded” error?

Many hosting owners are often unaware of what occupies space in their account.

We’ve seen old backups, obsolete apps, old mails, spam, unused media (images, videos), and even PC backups taking up a lion’s share of hosting space.

Here at Bobcares, we follow a systematic approach to troubleshooting Mail quota errors.

We list down the space usage against each folder, and then drill down the biggest users until we find what exactly is taking up the majority of disk space.

To save your time, we’ve here listed down the top causes we’ve seen for this error:


1. Uncleared Trash or Spam folder

Some hosting users get hundreds of spam mail a day.

Each mail may only be less than 100 KB in size, but over a period of several months, these mails can together consume hundreds of MBs or even GBs of space.

This usually happens for customers who use the Spam quarantine feature, and forgets about it. For these customers we recommend automatic deletion of spam mails.

But there are a few who wants to review the spam mails.

For such customers, we setup mail directory expiry settings, so that any spam mail that’s older than 30 days is deleted automatically.


2. Unmaintained IMAP account

These days, email users check their mails from multiple devices such as Laptop, Mobile, Home PC, etc.

To keep the mail synched with all their devices, these customers use IMAP instead of POP.

But we’ve seen some of these accounts retaining years worth of mails, with even large attachments (video, images, docs).

Often these mails may be required for references, and cannot be deleted.

We solve this in two ways:

  • POP old mails – We help mail owners configure their office mail client to download all mails older than 3 months. In this way, customers can always access recent mails, and if needed, old mails are still accessible.
  • Setting up a collaboration suit – Some customers use their mail Inbox as a shared folder (eg. sales, billing, etc.). For these customers, we setup a collaboration suite where mails and mail threads are always accessible over a web interface.
  • Increase quota – Some users still need old mails from all devices. For these customers we increase the hosting space quota.


3. Misconfigured POP3 account

By default, all POP accounts are configured to download mails (meaning no mails will be stored on the server).

But we’ve seen some customers set their mail clients to not delete mails from server (eg. some IT person setting it that way).

In such cases, if the customers say that they don’t need a copy in the server, we help configure the mail client to auto-delete POPed mails.


4. Unused “Default” or “Catch-All” address

Business mails can get lost if the sender mistyped an email address.

Eg. By typing “” instead of “”.

Some hosting administration tools provide a method called “catch-all” to capture those mails instead of sending it as a bounce-back.

But the problem with that it, the catch-all will capture all spam mails as well.

Eg. if someone sends a mail to, that will also be delivered to the catch-all address.

We’ve seen that most hosting users stop checking this catch-all address, and soon this account grows to several MBs in size.

In cases where we find catch-alls taking all the space, we delete all mails (or ask customers to download them), and then disable the catch-all feature.


5. Hosting space exhausted

Every hosting user gets a quota of space to store web, database and mail files.

We’ve seen many cases where this space is exhausted, leaving no space for new mails. Some common reasons for hosting space overage are:

  • Old site backups – Many customers restore backup archives to get one or two files, but then forget to remove the full archive. We’ve seen accounts with many versions of uncompressed archives occupying more than 70% of the space.
  • Unmaintained applications – Some customers try out various applications (like groupware, forums, etc.), but then forget to remove them from the account.
  • Unused media files – Video and image files are huge space users. We’ve seen sites storing several versions of the same video, audio or image files, which has not been accessed in several months or even years.
  • Database dumps – Website developers usually take backup of the database before they upgrade an app. We’ve seen several months worth of database dumps in some accounts that take up over 50% of space.
  • PC backups – Uncommon as it is, we’ve also seen some customers uploading files from their PC as a safe backup. This includes videos, audio, documents and images.
  • Old sub-domains – Some hosting administration tools allow creation of multiple domains under the same hosting account. We’ve seen unused sub-domains with many apps stealing away all the space from a working domain.
  • Misconfigured backup programs –  Many web apps such as WordPress have backup utilities. Some of these tools allow users to store the backup in the same directory, causing the space to get exhausted fast.


How we prevent “550 MailBox quota exceeded” error

Here at Bobcares, we believe prevention is better than cure, which is why we help customers configure their account to prevent a future mail quota issue.

We do this by setting up automatic to hosting account owner when the email quota or hosting quota reaches 80%.

This helps users to proactively login to their accounts and delete files before a mail bounce can happen.



550 MailBox quota exceeded is a common email error in web hosting servers. Today we’ve seen the top 5 reasons for this error, and how Hosting Support Engineers here at Bobcares fix them.


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Bobcares is a server management company that helps businesses deliver uninterrupted and secure online services. Our engineers manage close to 51,500 servers that include virtualized servers, cloud infrastructure, physical server clusters, and more.