configuration of multiple IPs for a jail

[tom at diogunix.com]

Greetings to the community. That's my first post to this list.
I run a mailserver (postfix/dovecot) in a jail on a 7.2 stable system.
My question is about configuring multiple IP addresses for that jail.
My IP configuration is just done via 
# jail blabla 123.123.123.249,123.123.123.227,123.123.123.248 blabla

I want to use 123.123.123.249 as my primary IP within the jail and futhermore 
use the same IP for outgoing SMTP connections.

Everything works nice so far. The only issue is, that postfix obviously insists 
to use the second IP (227) to send out the Emails though it should use the 
primary IP (249). Trying to bind postfix to the right address did not help. 
I've read tons about jail configuration but could not find the one hint needed.

So my question is:
Does a jail always use the 'lowest' IP from a bunch of multiple IPs given with 
the jail start command ? I can't find any other explanation. Nothing else 
points to the 227 address. And if true - is there a way to change this 
behaviour ?

Thanks a lot in advance
Tom