Just moved to a new server and on threads for which users have e-mail notifications set for (favorite threads), we're getting the following error:

Fatal error: Call to undefined function: mail() in addpost.php on line 869

Any ideas?

Thanks in advance!

mail() is a built in function of PHP which threads uses to send email. If you're getting an undefined function error with it - you'll probably need to ask your host. Something isn't setup right with php on that server.

Most likely they need to verify settings in their php.ini file.

Thanks... will look into that.