HTML emails used to work just fine on my last server, but now the emails just show the HTML code as text.

The last server was running RedHat 9, PHP 5, and Sendmail. The new server is running Plesk 7 Reloaded, PHP 4.3, and Qmail.

Any ideas what's going on here? I'm guessing it's a PHP setting or perhaps a Qmail issue, but I can't figure out where to look.

Use your script and immediately take a look at your /etc/httpd/logs apache error log!

I've found qmail is more stringent with what it is given via scripts, particulary in the mail header! So look there for an error.

Had this problem recently myself, has to do with the way qmail handles carriage returns.

If you're using any rn, change these back to n as qmail automaticaly replaces the n with rn which breaks stuff.

G'luck with it.