I am using the latest version of Pegasus. I wrote a long email today and ran the spell check. It flagged every work, including common words that were correct.

What is going on?

Verify that your spell checker is configured to use the appropriate dictionary (see image below).

Also, you said that you are using the latest version of Pegasus Mail which is 4.80 however that version has a bug that breaks the saving of user defined words in the spell checker. The 4.81 public beta fixes that problem. Its only known issue of significance affects users whose Home and New mailbox directories are different, which is uncommon.

Thanks; will check and correct.