I did notice one problem, which may have had more to do with my machine’s configuration behind the NAT router I use for connecting to the Internet, but I found that I could not send mail (for example, using the eForm snippet) until I followed some advice I found on the PHP documentation’s user comments:
If you’re using a linux server using Postfix, and your server hasn’t the host name set to a valid name (because it’s behind a firewall in an intranet), it’s possible that when sending mails using the mail function, some mail servers reject them. This is because they can’t check the return path header. If you want to change the Return-Path used by sendmail init the php.ini and edit the sendmail_path variable to this:
sendmail_path = "sendmail -t -i -F email@example.com -f firstname.lastname@example.org"
I added this line to the php.ini file for PHP 5 (the sendmail_path line was commented out in the default php.ini file), and am now having no problems sending/receiving mail. I also updated MODx’s copy of /manager/includes/controls/class.phpmailer.php and class.smtp.php to the latest, 1.7.3.
Actually, I think the problem wasn’t that I couldn’t send mail, it was more likely that my POP server wouldn’t accept it without the proper headers. In any case, after the fix to the php.ini file and the new class files, the mail goes through.