I would like to whitelist any sender that a user on my mail server has sent an email to. Overriding some spamchecks,greylisting etc, depending on where it is in the smtpd_recipient_restrictions order.
I do not believe there is a solution out of the box. But postfix gives you the tools to custom build this behavior. You would need to setup your own database to track the relationships between user and foreign address. Then you can write two scripts to use with check_policy_service. One script on the submission side for when mail is sent to grab the rcpt address and store it in the database. The second script on the smtp side for "incoming" mail, if the script finds the mail-from address associated with the rcpt address then return OK to accept the mail.
There is an example grey-list script doing similar to this at the bottom of http://www.postfix.org/SMTPD_POLICY_README.html You can see the values your script can return on http://www.postfix.org/access.5.html
If someone else can chime in if I'm wrong on this part, but I'm 99% sure a result of OK (vs dunno) accepts the mail and stops further checks for the smtpd_*_restrictions section the check_policy_service is used in.
PS. Another more complex option would be using your own built milter to do the same behavior as a policy script would.
