I’ve tried several fonts. It makes no difference in the line spacing.
There is no vertical line spacing adjustment in the compose window I’m aware of currently as advised further up, but there is however a feature request for that by another user via this link.
no matter what font I chose (and I do remember to SAVE), it doesn’t change the font in the next email I begin. That wasn’t happening yesterday.
If changing the font & style and size is not changing in the compose after saving settings when you begin your next email, then sounds like some default setting has changed in the program somewhere.
Try closing all your eM Client windows “apart from the main GUI” and then right click in the body of any email and select Zoom / Original on the menu.
Then open a new compose window and type some text and then again right click and select Zoom / Original. Next close eM Client. Then reopen eM Client and try changing the default compose font in Settings / Mail / Compose section, and then see if they stay changed when you begin a new email.
Failing that, if you made a previous day eM Client backup either manually via the menu or setup automatic periodic backups via the Settings, try restoring the backup via “Menu / File / Restore” where it then will be the same as on that day.
Now if you haven’t made any eM Client backups yet since installing eM Client, then suggest to just try “uninstalling the program” and reinstalling and see if that fixes it.
If you have Windows when uninstalling, “don’t delete the database” when asked on the uninstall wizard, and then re-download and install “the same or later version” of eM Client via the release history page.
If you have a Mac just close eM Client and “drag the eM Client icon in Applications to the bin”. Then download and install eM Client again also via the release history page “which will also pickup your existing database”.