If your Thunderbird inbox seems to be full of spam, why not start marking emails as junk. You can skip an extra step by sending them straight to the trash as well.
Thunderbird is equipped with a junk email folder that spam and garbage mail goes to by default. The problem is, emails in the junk folder just sit around and take up space until you manually go in and delete them. If you’re careful about what you mark as junk, you won’t need to worry about this folder. Here’s how to send emails that you mark as junk directly to the trash.
Automatically Delete Junk Mail in Thunderbird
Open Thunderbird and select Tools > Options.
In the options window, click the Security > Junk tab. Then check both “When I Mark Messages as Junk” and “Delete Them.” Click OK to save changes.
Now emails that you mark as junk or spam will go straight to the trash and no longer occupy your local disks.