Some Questions about Foritimail. Basic concept.

[joesnow]

Hi, guys,      I'm new to Fortimail, and my boss asks me to research Fortimail and take it as an replacement of opensource  solutions. Here are unresolved questions after I read the cookbook carefully.      1. We use postfix  and dovecot as email sevices, and I want to use fortimail gateway mode. So basically, I need to configure public DNS record, MX/A/PTR to point fortimail as fortimail.xx.com and 202.108.x.y and internal dns MX/A/PTR records too. When external MTAs send emails to me, it goes through Fortimail via DNS queries. That makes sense. But how does fortimail interactive with my email servers and delivery incoming emails to my email server?      2. MUA(outlook, foxmail.etc) needs to authenticate, and SMTP authentication is also required when sending emails. It's easy to configure without fortimail, postfix and dovecot rely on backends(LDAP/AD/MySQL.etc) to authenticate and query user's mail address and quotas and mail locations.    But how to do it with fortimail?     3.  Regarding outgoing emails, how does my email server know outbound emails would go through fortimail? Let's say my mail server is 172.16.234.11, when I use outlook to send out an email to my gmail, it would query DNS and find out gmail's SMTP and delivery it via the gateway . How does fortimail intercept the traffic ?   Thanks very much guys.