I had lots of messages in my Thunderbird mail accounts. More than 1200 send messages and more than 1500 incoming message. The send messages alone had a size of more than 25 Megabytes while the incoming messages a combined size of more than 800 Megabytes.
I made the decision to archive old messages to free up disk space, and maybe also improve the performance of the email client in the process.
The best way in my opinion is to archive all old messages that I do not need anymore and remove them from Thunderbird completely. After thinking about the how-to for a while I found a method that works perfectly.
Thunderbird creates so called mail folders in its profile folder. Inside those mail folders are files without an extension and msf files of the same name.
The idea was to create a new folder, name it accordingly and move it out of the Thunderbird profile folder. I created a folder sent-071101 and moved all sent mails into the folder that were older than one month. This can be done by simply dragging and dropping mails into the new folder.
After doing that you close Thunderbird and go to the profile folder, normally located in the Application Data of the Documents & Settings folder.
I did create a new folder mail-backups and moved the files sent-071101 and sent-071101.msf into it. The mails that have been moved into that folders are not shown in Thunderbird anymore. I simply proceeded with other mails that I did want to archive and repeated the process again.
This is also an excellent way of backing up your emails regularly. Just copy all those files from the mail folders to another location or burn those to DVD or CD.
Finding the Thunderbird profile folder:
The Thunderbird profile folder is by default located at C:\Documents and Settings\van dread\Application Data\Thunderbird\Profiles\XXXXXX.default\Mail\
In newer versions of Thunderbird, you can select Help > Troubleshooting Information > Show Folder to have the folder opened for you on your system which should speed things up a bit.
Update: You can alternatively use a software program to archive emails in Thunderbird to speed up the mail client.
While the manual method works fine, you may want to use the email backup software instead. There are some reasons for that. A core reason is that you can still access all those backed up emails, and also search them. You cannot do so when you use the manual method.
Other options include that you do not end up with new files whenever you decide to create an archive of old messages, as everything is contained in one program instead.
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