As of 2024, emails are typically received through Internet Message Access Protocol (IMAP) servers, where the individual emails are kept in a centralised storage. This has the advantage that you can access them from several email clients or devices and always see the complete set of emails in the same state as you left them (directory structure, read status, labels). For instance, you can use your work computer, laptop, phone, or a web interface to access them¹.

However, a common problem is that the email storage space offered by an email provider is limited, typically to several gigabytes. Depending on email usage, one commonly reaches the allowed email storage quota after a few years. The more emails one sends or receives that include large attachements, the quicker the storage space runs out.

Fortunately, it is straightforward to archive older emails, which means moving them to local storage and deleting them from the provider’s IMAP server, thereby freeing up disk space on the server. Namely, one moves the old emails to local storage (e.g. to your laptop) and deletes them from the IMAP server. This way, the archived copy will only be available on that particular local machine (e.g. your laptop) and the other devices will not be able to access the archived emails any more.

Archiving emails is straightforward and convenient using the Thunderbird email client.

• Start Thunderbird. I assume that you have configured email access already.

• Navigate to your “Local Folders” -> Archives in the left navigation pane.

• Create a folder named after your email account from which you want to archive emails, e.g. user@cnrs.fr, under the Archives folder.

• Select your user account on the left side. Go to Settings -> Copies & Folders -> Message Archives. Select “Keep message archives in” and select “Other”. Select the folder you created in the previous step in “Local Folders”.

• Click on “Archive Options” and select “Yearly archived folders” and “Keep existing folder structure of archived messages”. This will keep the archived emails in folders separated by year and retain the folder structure in your inbox, e.g. mailing list sub-folders.

• Confirm the changes.

• Go to your inbox and sort the emails by date. Select the emails from previous years and click on “archive”. The old emails will be moved to the local storage and removed from the IMAP server. This can take some time, depending on the number of emails affected and your internet connection speed.

• Repeat the step above for any emails you want to archive. The IMAP server storage should free up significantly.

• Repeat the last few steps for any other email account for which you want to archive emails.

This process works very well for me.

Cheers.
 Fabian