Thunderbird IMAP Folder Problem

Thunderbird IMAP Folder Problem

Benefits of IMAP

The IMAP protocol supports both online and offline activity. Therefore, messages can be stored both on the local machine and on the server, enabling numerous benefits:

  • Multiple clients can be used to access messages. For example, a Thunderbird user with a Microsoft Live account can use both the Thunderbird application that is installed on their system and the web-based interface provided by Microsoft.
  • Thunderbird users can download their messages to their local system and access them even when they are not connected to the internet.
  • Messages load faster when they are stored on a local drive. Search performance is much faster than searching a set of messages on a remote server. Full-text search of a message body is only possible on messages that have been downloaded.

In order to provide this kind of flexibility and functionality, though, messages must be synchronized between the local machine and the email server.


To understand message synchronization, consider the following scenarios:

  • A message is downloaded to Thunderbird and deleted in Thunderbird. (The message must be deleted from both the local machine and the email server.)
  • A message is downloaded to Thunderbird and later deleted by a web-based client (such as Yahoo Mail or Gmail). (The message must be deleted from the Thunderbird message repository.)
  • A draft message is composed and saved (but not sent) in Thunderbird. (The draft must be copied from the Thunderbird message repository to the email server.)

Whenever Thunderbird starts, it checks the state of synchronization between the Thunderbird message repository and the email server, and then performs any transfers that are necessary (such as downloading new messages from the server, deleting from the server any messages that have been deleted locally, etc). Thunderbird continually synchronizes with the email server as long as it is running and has access to the internet. If internet access is lost, Thunderbird will synchronize when access is reestablished.

Non-synchronized messages are still accessible within Thunderbird. The only difference is that rather than downloading the entire message, only the message “headers” are downloaded. (Message headers contain information like the sender, recipient(s), subject, etc – everything except the body of the message.) The message body is not downloaded until you click on the message in the message list (which means that if you are not online, you can’t read the message).

Synchronization impacts performance and disk space usage.

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