Hello – I've got 251 GB of Flash Storage and almost all of it (~ 3/4) is consumed by Mail. I've got like 30,000 msg's in the mail app. Have tried numerous times to delete hundreds if not thousands of the msg's, even prioritized deleting one's w/ attachments 1st. When I shut down and restart it seems like the system freed up 4 or 5 GB, then as I run the Mail app, and subsequently check storage an hr later via the About This Mac window, i find that the available storage has dwindled again to less than 1 GB.
I told a mac-enabled friend and he's like, 'yeah, those msg are deleted but they're not gone off ur machine' (?). Note – I'm emptying trash on a regular basis.
Have taken to running Google Mail via Web so as not to take up space consumed by running Mail App (still only have 2.5 GB storage available), but miss the ease of Mail app.
I did take a quick run thru Storage posts in the forum and bought High Sierra for Dummies book, still couldn't get to corrective action. Help, plz