Text smiley faces show up as the letter J in emails

What you read is correct. When you type :) in Outlook, the :) is removed and replaced with 0x4A Wingdings font, which gets converted to HTML markup in the email.

This maps to exactly "J" in common alphabet fonts, and so that is what you see if your email client does not follow the font face directive in the email (most other than Outlook) and/or you don't have wingdings installed.

Your best option is to just mentally map a solo 'J` to a smiley face.

Found a solution to this:

Macs already have a Wingdings font, but it's not set up for typing... it appears to just be available for use as glyphs.

I've taken my Wingdings font and re-saved it using Font Forge. This way the key mapping actually works (Though I'm not sure what functionality is lost by doing this).

Here's how to get setup:

1. In Finder, go to: Macintosh HD/Library/Fonts
2. Find Wingdings.ttf, right click to open "Get Info"
   1. Scroll down to "Sharing & Permissions:"
   2. Click the lock icon in the bottom right to unlock.
   3. Give user "everyone" "Read & Write" permissions
3. Close "Get Info" and move Wingdings.ttf to a different folder. I would have preferred simply renaming the font, but it wouldn't let me.
4. Download my re-saved font: https://github.com/bzle/J-to-Smiley-Fix/raw/master/Wingdings.ttf
5. You may be able to add this font where the old one was removed from... I added this as a user font via Font Book. It gave an error saying it would be a duplicate font, but you can just check the box and add anyway.

At this point I restarted Airmail (not sure if that was necessary), and now the J is a smiley!