Update postfix.sh, so mysql_sender_dependent_default_transport_maps.cf is in line with mysql_sasl_passwd_maps_sender_dependent.cf

[freimuts]

• I've read the contribution guidelines and wholeheartedly agree them

What does this PR include?

Short Description

In case when the domain has relay host configures (rh.example.com) and you configure a separate relay host for user within that domain (rh2.example.com) credentials for relay host are selected from domain relay host (rh.example.com) no users, like:

[at]example.com - relay host rh.example.com
example[at]example.com - relay host rh2.example.com

Expected result:
When sending email from any email under domain use rh.example.com, when sending from example[at]example.com use rh2.example.com, both hosts require authentication, correct authentication is provided and email sent.

Actual result:
When sending email from any email under domain use rh.example.com, when sending from example[at]example.com use rh2.example.com, authentication credentials for rh2.example.com are selected from rh.example.com.

Cause:
mysql_sender_dependent_default_transport_maps.cf SELECT COALESCE starts by relayhosts LEFT OUTER JOIN mailbox and then uses relayhosts LEFT OUTER JOIN domain, but mysql_sasl_passwd_maps_sender_dependent.cf currently does opposite, so I flipped the order so that both queries have same logic.

Affected Containers

• postfix

Did you run tests?

Yes

What did you tested?

I tested postfix, sending, receiving mail using relays and not, relays in different configurations. Since I have used this fix in production for about two weeks now.

What were the final results? (Awaited, got)

The connection was always made and authenticated correctly.