I know this is a bit of and old post to reply to, but I just wanted to clear up some stuff for postfix as there seems to be a bit of confusion.

Tony Earnshaw wrote:

Ummm, no it doesn't. The local transport (by deafult) handles all mail to mydestination. The local transport processes aliases and .forward and then (if still necessary) delivers the mail to disk. The way it which it delivers the mail to disk is determined by (from http://postfix.org.cn/postconf/mailbox_command.html):

The precedence of local(8) <http://postfix.org.cn/man/local.8.html> delivery features from high to low is:aliases, .forward files, mailbox_transport <http://postfix.org.cn/postconf/mailbox_transport.html>, mailbox_command_maps <http://postfix.org.cn/postconf/mailbox_command_maps.html>,mailbox_command <http://postfix.org.cn/postconf/mailbox_command.html>, home_mailbox <http://postfix.org.cn/postconf/home_mailbox.html>, mail_spool_directory <http://postfix.org.cn/postconf/mail_spool_directory.html>, fallback_transport <http://postfix.org.cn/postconf/fallback_transport.html>and luser_relay <http://postfix.org.cn/postconf/luser_relay.html>.

mailbox_transport should be a transport listed in master.cf. Your line above is perfectly correct. mailbox_command should be something like /usr/local/bin/maildrop -d "$USER" -f "$SENDER"

They are almost equivalent. The only difference I can see is that the mailbox_command will be executed with the permissions of the recipient, implying that the user must be in the passwd db. The mailbox_transport the command (in master.cf) will be executed as the user specified in master.cf and is reposible for finding out permissions and changing user itself.

If I were only delivering to local users, I'd be inclined to use mailbox_command.

Ummm, not really. This entry in master.cf specifies a postfix transport (a method of delivering mail) just like local and virtual. It does not get used by virtual, but can be used instead of virtual (since postfix's virtual and maildrop do much the same job really). There are multiple ways of using transports in postfix and describing them all would be more confusing than helpful, but a couple of main methods are:

To get maildrop to deliver to all of the virtual users (domains specified in virtual_mailbox_domains): virtual_transport = maildrop

Otherwise, to get postfix to use (not use) maildrop or a per domain (or per user for 2.*) basis, use the the transport table with contents like: maildrop.domain.com maildrop virtual.domain.net virtual

see transport(5) for more info

I hope that clarified something. For more info (and maybe a better explanation) look at the postfix docs. I would recommend starting with http://www.postfix.org/ADDRESS_CLASS_README.html and following links to relevent stuff from there.

Jeff