We’re going to use Thunderbird to show how to do this, however you can implement the same general idea with just about any mail application, like Apple Mail or Windows Live Mail.

If you are using Outlook with IMAP there are more specific instuctions: Choose How to archive IMAP messages in Outlook 2007/2010/2013 from the email FAQ.

If you’ll be using a different mail app, the steps below won’t be 100% precise, but the same general idea should apply.

Create local archive folders

Although I’ve got a few server-side folders, I like to merge everything into one off-server archive folder for all messages (except Sent emails) because I can always search for emails later on. In other words, folders for separate emails may simply make things more complicated than they need to be. You can choose to create as many off-server folders as you like for archiving, but it will make more work to set-up.

1. Right click on “Local Folders” on the left in the Thunderbird folders pane.
2. Choose “New Folder”
3. Give it a name — I called mine “Archive”. It should be a subfolder of “Local Folders” already, but if it isn’t, be sure to select that option.
4. Press Create Folder

You will now see a folder called “Archive” (or whatever you named it) under “Local Folders” in the left sidebar.

If you’d like to use multiple categorized archive folders, you can repeat the process above to create each one of them.

Move server-side emails to local archive

Now it’s time to move your emails from the server-side folders to the local (off-server) archive folder.

1. Under your IMAP email account in the sidebar, find the folder you wish to archive emails from and select it.
2. Select all the messages you wish to archive (such as all those older than 90 days) and drag them to your folder of choice under “Local Folders”. In the example I used above, this would be the “Archive” folder, but if you created your own folder name(s), you can choose one of those.

You can follow the same steps above for any or all of your mail folders. For example, create a “Sent Archive” and drag and drop all of your old Sent emails from the IMAP folder into the Local Folder.

That’s it! Note that it might take some time for your mail app to download the full copy of each email, especially if your Internet connection is limited in speed. Give it time!