This doesn't happen for me, so I assumed there must be a setting to turn that off. But looking through the FastMail settings I cannot find anything like that.

This doesn't happen for me, so I assumed there must be a setting to turn that off. But looking through the FastMail settings I cannot find anything like that. Still, I don't see any yellow smiley face icons in FastMail when I send or receive ":)" in emails.