TexMath is no longer working

It's not a general problem (it's working for me). Is the TeXMath bundle enabled in the Bundles preferences pane? Also try writing texmath instead of math.

Has it ever worked for you?

It seems to work on my laptop, but it doesn't work on my desktop.

Texmath is enabled in the Bundle preferences.

Try launching MailMate from a Terminal window to see if you get any (helpful) error messages:

/Applications/MailMate.app/Contents/MacOS/MailMate

Not really.

This is the closest that I got.

Warning: Failed to run command (Error: no lexer for alias 'math1104DDFF-E171-4A75-B3CC-9CE4004CC1BD' found
):
#!/bin/bash

STYLE=`defaults read com.freron.MailMate MmDefaultPygmentsStyleName 2>/dev/null`
"${MM_BUNDLE_SUPPORT}/vendor/pygmentize" -f html -O noclasses=1,nowrap=1,style=${STYLE:-colorful} -l "${CODE_LANGUAGE}"

Warning: Failed to do code styling.

Something goes wrong when MailMate temporarily removes the math in order to process it separately and then re-insert it. The result is that it thinks the language is math1104DDFF-E171-4A75-B3CC-9CE4004CC1BD instead of just math. Does it work if you insert some newlines? (I don't need that for it to work at my end.)

I'm thinking that maybe some combination of settings in the Composer preferences pane triggers this bug, but it's not obvious exactly how. Could you write me via “Help ▸ Send Feedback” and I'll provide some additional instructions on getting more (messy) debug output.

I had a similar problem but figured out that the option "Math language: Tex to Math", was not selected in Preferences > Composer. That fixed my problem.