what does postfix use to send mail?
 

i have a forum and my ISP's SMTP server sort of died so it stopped emailing people. i set the board to email using sendmail located at /usr/sbin/sendmail and it would just not email. i changed it to /usr/sbin/postfix and it still would not send mail. i changed it to use SMTP and i listed the smtp as shawnserver.d2g.com (the same computer the forum is on) and now it actually sends mail with no problems at all.

i have postfix installed and the only way i can seem to send anything is through it with the command "mail -s subject user" or by specifying my computer as an SMTP server.

i know that it is postfix sending mail because i tried to send an email from my newly created IMAP account and i got it returned saying that the person i was mailing did not exist, the header on the return message was "from postfix mail service"