This article explains how you can keep your mail server under your storage's limit and what you can do if you get a warning like "over quota", "quota exceeded" or "mailbox for user is full".

What is your server quota?

Most of the mail servers have a storage limit that you cannot exceed. It can vary from server to server, but it is generally around 100-500 MB on corporate's servers and almost unlimited for some popular free mail providers like Gmail (which offers more than 7600 Mb), Yahoo! (unlimited) or GMX (unlimited).

How can I know my server quota?

It depends on your server. If you use a free mail server or your ISP's mail server, please search on its support articles. If you use a corporate mail server, you may ask your administrator.

Last, if you use an IMAP account which provides indication of its quota (this is not always the case), you can either:

• check if the quota is indicated in your folder's properties. Right click on your Inbox folder, select Properties and then the Quota tab.
  
  
• simply wait until Thunderbird displays a quota indication in its status bar. It is only shown when it is useful, which is not before your storage capacity is over 75%.
• use the Display Quota add-on in order to display the quota directly in thunderbird's status bar.

How can I decrease the size of my emails on the server?

In order to do some clean up, it's good to have good indicators of:

• how big are your folders?

Folder size is not indicated in Thunderbird, so you need to install an add-on in order to display it. You can either choose Mail Summaries or Extra Folder Columns.

• how big are your mails?

Simply check that you have chosen to display the Size column in the Message pane. If you don't, please read the Message List Columns article to add it.

POP server

On a POP server, all the incoming messages are downloaded to your computer. Depending on your choice, a copy of your messages can stay on the server until you move them to another folder or delete them, or until a certain time. So if you need to free some space, you should consider to:

1. Check the current size of your Inbox folder.
2. Delete some of your old email in your Inbox folder, especially the larger emails. Sort your messages by size in order to easily detect which of them take the most of space.
3. Archive your older mails in order to move them out of your Inbox, and consequently to delete them from the server (but keep them locally).
4. Check the new size of the Inbox folder in order to be sure that it has decreased has expected. If this is not the case, compact the folder (from the File > Compact Folders menu).

IMAP server

On an IMAP server, all your messages and folders are synced between Thunderbird and your mail server (please read the IMAP synchronization article for more details). So if you need to free some space, you should consider to:

1. Delete some of your old email in all your folders, especially the larger emails. Sort your messages by size in order to easily detect which of them take the most of space.
2. If you want to keep a copy of your mail but don't need the attachment anymore, you can simply detach the attachment from the mail, because attachments generally take most of the space.
3. Archive some of your older mail. However, if you simply move them to another folder on your IMAP server, you won't win back any space. To resolve this, you need to set your "Archive" folder under your "Local folders" account and not as a subfolder of your IMAP account.