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.
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.
Wietse
