Latest mail version for Mojave 10.14

Safe Boot from the HD, (holding Shift key down at startup), does the problem occur in Safe Mode?

Safe mode attempts to repair Disks & clears lots of caches, so if Safe Mode works try again in regular boot.

If still no good...

Quit Mail & login to your WebMail in a Browser, do they appear that way on the Server?

If you have no POP accounts & they’re all IMAP accounts then in Mail’s Mailbox menu choose Rebuild.

The version of Mail is generally tied to the MacOS version, are you having a problem?

Any luck yet?

Just thinking, maybe you have a bad font?

What font is Mail set to use in Mail>Preferences>Fonts & Colors?