Mozilla Thunderbird is one of the most popular email clients, and we recommend it to our customers instead of Microsoft Outlook. We are quite satisfied with Mozilla Thunderbird, but even this email client has a problem that the developers have not yet resolved.
If you use Thunderbird for an extended period via IMAP, occasionally adding and removing accounts, and work with a large mailbox (tens of GB), all your activities are stored in the cache on the disk. Unfortunately, Thunderbird does not include mechanisms to clear the cache, so everything remains on the disk permanently. After a year of use, you could have over 100 GB of Thunderbird cache on your disk.
Fortunately, there is a useful add-on for Thunderbird called Clear IMAP Local Cache, which clears the cache every time Thunderbird is loaded. The add-on deletes already removed accounts, downloaded attachments, and other data from the disk. By deleting downloaded attachments, you won't lose the attachments themselves, as they will be deleted only from the cache and remain on the server, from where they can be downloaded again.