Greg Sims:
> We are seeing: "has exceeded the maximum number of connections" in our
> logs for domains associated with outlook.com.  We have a transport
> named "outlook:" in transport.regexp as follows:
...
> This transport is configured as follows in master.cf:
> 
> outlook  unix  -       -       n       -       6       smtp
>   -o syslog_name=outlook

Are you using this for all outlook email, or only for u...@outlook.com?

Note: this is a trick question.

> We would like to use Per-Destination Connection Caching to increase
> our throughput for "outlook:".  Our mail server does not specify
> "relayhost =" in main.cf.  Is it possible to associate per-destination
> caching with the "outlook:" transport?  If not, what is the best
> alternative?

Did you mean:

master.cf:
    outlook  unix  -       -       n       -       6       smtp
       -o syslog_name=outlook 
       -o smtp_connection_cache_on_demand=yes
       -o smtp_tls_connection_reuse=yes

It's easier to do the reuse configuration in main.cf.

main.cf:
    smtp_connection_cache_on_demand=yes
    smtp_tls_connection_reuse=yes

Note that Postfix has "smtp_connection_cache_on_demand = yes" by
default, but for TLS you have to turn it on because that is still
relatively new. Sofar there haven't been problems with reusong
TLS encryted connections.

> If the answer is something like the following in main.cf:
> 
> smtp_connection_cache_destinations = hotmail.com, hotmail.es,
> hotmail.co.uk, outlook.com, outlook.es, live.com, msn.com

You don't want to do that unless you must exclude some destinations.

> should we try to include All the domains associated with "outlook:" so
> even small volume domains are not counted as connections by
> outlook.com servers?  If this is the case, should/can we point
> "smtp_connection_cache_destinations =" to a regexp file?
> 
> We are not seeing "conn_use=" in our logs.  Is it true that Postfix
> will not log "conn_use=" for current releases?  We are running
> postfix.x86_64 2:3.3.1-12.el8.

See above. You need to turn on smtp_tls_connection_reuse.

        Wietse

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