From MozillaZine Knowledge Base

This article was written for Thunderbird but also applies to Mozilla Suite / SeaMonkey (though some menu sequences may differ).

If you have received an alert saying that new messages have arrived but there are no new messages in your Inbox folder and you didn't get an error message, see if any of the following apply.

• Make sure the drop down View menu is set to "View all messages."

• For POP accounts, check to see if you have Thunderbird set up to automatically download new messages.

• IMAP accounts support multiple email clients reading messages in the same mailbox. If you read the message using one email client that message will appear as read in the other email clients.

• Thunderbird may have run into a problem downloading a "bad" (malformed) message. There is also a bug that can cause a similar problem (with some POP servers) if there is a pattern of certain control characters in the message body. You can workaround this by using webmail (a browser) to read and then delete the "bad" message. This should free up the logjam and let Thunderbird download any other new messages the next time it checks for new mail.

• See Disappearing mail.

• If you see a "Building summary file" message (in Thunderbird's status bar) for a long time, or if nothing else listed above seems to be the problem, try this workaround.

See also

• Checking for new messages in other folders
• Unable to write to the mailbox
• Folder is being processed