post by email cuts off content following an apostrophe

That’s really odd, I’ve never seen that before.

If you create another email with an apostrophe in a different position, where does it break?

I’ve tried all kinds of stuff now in testing. It always, every time, breaks at the first apostrophe.

I’ve tried disabling plugins (I thought maybe Markdown on Save Improved was messing with stuff), but even with all other plugins disabled, no dice.

Any thoughts about where else to look?

Any further thoughts?

I’m open to the possibility that the problem is in my server config, but I’m not sure where to begin looking…

I don’t have any good suggestions off the top of my head, unfortunately. The first thing I’d debug is the value of $message right before it’s passed to wp_mail(). If it’s intact, then the problem is either in wp_mail(), PHPMailer, or whatever utility you use to send emails on your server.

Another thing you could do to debug is set up your WordPress install (with all plugins) on a completely different server environment and see what happens. If it reproduces, it’s probably a code issue. If not, it’s probably a server issue.