So you're having troubles Emailing a password protected pdf from within the program?  Im not sure why foreign based would be any different for emailing.

Maybe something here will help?  It mentions Thunderbird.

https://proconnect.intuit.com/community/manage-integrations/help/set-or-change-default-email-program...

I personally don't use the Proseries Email function.  I save to PDF then use Bullzip to password protect with a password of my choosing then attach to email like any other file.