I need to know how to fix the corrupted database.
If you have a Mac, to repair eM Client database do the following.
Close eM Client and then “open the Terminal app via either Launchpad or Utilities” on the Mac. Then Paste and run the following command.
/Applications/eM\ Client.app/Contents/MacOS/eM\ Client /dbrepair
Then reopen eM Client and see if that helps.
If the slowness is due to too much historical data in the database, it is a problem because I need to keep all those emails, and starting all over is not helping me.
If the repair doesn’t make any difference and you create a new database and setup new “and that fixes the problem” but you then don’t have old Local Folder messages, then you can then do a “Partial Restore” to get those old database Local Folder messages back to your new Database Local Folder messages by following either my post below or the official eM Client blog page.
How to do a Partial Restore
https://forum.emclient.com/t/emails-missing-from-backup-when-restored/101556/2
eM Client official blog page Partial Restore
https://www.emclient.com/blog/how-to-restore-backup-in-em-client-614
Lastly if this issue has only happened recently “and you have been making regular eM Client backups”, then you can alternatively try restoring a recent dated eM Client backup when you know it was working ok via “Menu / File / Restore”. Then any new emails since the backup date will restore when eM Client recconects online.
Note: If you do try restoring a recent dated backup, make a manual backup of your current database first via "Menu / Backup incase you need to revert back for any reason. You can see when the backup is complete in Show Operations via clicking the drop-down on the right of Refresh top left.