postfix multi instance transport

Question

I'm configuring a postfix mailing server with multiple instances. Each instance has been assigned it's own ip and domain. For some of the instances, I've enabled rate delays for specific domains:

main.cf

yahoo_destination_rate_delay = 5s
yahoo_concurrency_failed_cohort_limit = 10
yahoo_destination_concurrency_limit = 10
ymail_destination_rate_delay = 5s
ymail_concurrency_failed_cohort_limit = 10
ymail_destination_concurrency_limit = 10

master.cf

yahoo      unix  -       -       n       -       -       smtp
    -o syslog_name=postfix-3
    -o smtp_fallback_relay=
ymail      unix  -       -       n       -       -       smtp
    -o syslog_name=postfix-3
    -o smtp_fallback_relay=

transport

yahoo.com    yahoo:
ymail.com    ymail:

My question is, how does each instance know which transport to use? i set

postmap /etc/postfix-3/transport

but is that enough?

It seems to be working but that could only be because a few other instances have similar transports. I'm afraid each instance could be reading an incorrect transport map. Should I assign each instance a specific transport file or is that assumed?

Thanks!

Answer 1

I don't know what you mean. Each instance has it's own folder under /etc/ and you have transports configured in each master.cf in each instance folder.

All instances are independent of each other and don't know each others configuration. Except the few configuration parameters that configure the instances itself.

Answer 2

This seemed to answer my question:

Mail transport switch

Once the trivial-rewrite(8) daemon has determined a default delivery method it searches the optional transport(5) table for information that overrides the message destination and/or delivery method. Typical use of the transport(5) table is to send mail to a system that is not connected to the Internet, or to use a special SMTP client configuration for destinations that have special requirements. See, for example, the STANDARD_CONFIGURATION_README and UUCP_README documents, and the examples in the transport(5) manual page.

Transport table lookups are disabled by default. To enable, edit the transport_maps parameter in the main.cf file and specify one or more lookup tables, separated by whitespace or commas.

Example:

/etc/postfix/main.cf:
    transport_maps = hash:/etc/postfix/transport
/etc/postfix-3/main.cf:
    transport_maps = hash:/etc/postfix-3/transport

I simply edited each instances main.cf and added the transport_maps option and pointed to the correct transport map. All seems to work ok.

source: http://www.postfix.org/ADDRESS_REWRITING_README.html