I'm afraid I haven't been much help. Email problems can be really nasty to solve, especially when QuickEmail is successful at sending the mail.
I can't think of anything else since the Forgot Password code should do exactly what QuickEmail does. I've spent many hours putting debugging statements into the MODX mailer and PhpMailer code and now usually just set the SMTP System Settings.
Even then it can still take a lot of time. I once spent most of a day trying to get mail to work on a localhost install and finally discovered that the SMTP host didn't like 'localhost' as a domain name.
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PLEASE, PLEASE specify the version of MODX you are using.
MODX info for everyone:
http://bobsguides.com/modx.html