> Looking at Noel's reply to a connection caching question, I realized
> (once again) that the cache is shared among all SMTP clients, even
> across SMTP clients of mail delivery transports.
This is not what happens. The SMTP delivery agent prepends its own
service name (the first field in master.cf) to the name of every
connection cache entry.
(This is easily verified by setting "scache -v" in master.cf, and
by comparing the logging with "default_transport=smtp" with the
logging of "default_transport=relay").
There is, therefore, no "leakage" of cached sessions from one
transport to another transport, and therefore no "violation" of
sender reputation policies.
> That is a good thing from a connection reuse perspective. It can,
> however, have an unexpected result when different SMTP transports
> have different smtp_bind_address settings. This is done, for example,
> to give different mail streams a different client IP address so that
> their reputations are "separated".
> The way that Postfix currently implements connection reuse, it is
> possible that different mail streams become mixed.
> A possible solution is that an SMTP client tags the connection cache
> with smtp_bind_address information (if non-default) so that it can
> be taken into account when searching the connection cache.