Compatibility with Postfix < 2.2 TLS support

Postfix version 2.2 TLS support is based on the Postfix/TLS patch by Lutz Jänicke, but differs in a few minor ways.

• main.cf: Specify "btree" instead of "sdbm" for TLS session cache databases.

  TLS session cache databases are now accessed only by the tlsmgr(8) process, so there are no more concurrency issues. Although Postfix has an sdbm client, the sdbm library (1000 lines of code) is not included with Postfix.

  TLS session caches can use any database that can store objects of several kbytes or more, and that implements the sequence operation. In most cases, btree databases should be adequate.

  NOTE: You cannot use DBM databases. TLS session objects are too large.

• master.cf: Specify "unix" instead of "fifo" as the tlsmgr service type.

  The smtp(8) and smtpd(8) processes now use a client-server protocol in order to access the tlsmgr(8) pseudo-random number generation (PRNG) pool, and in order to access the TLS session cache databases. Such a protocol cannot be run across fifos.

• smtp_tls_per_site: the MUST_NOPEERMATCH per-site policy cannot override the global " smtp_tls_enforce_peername = yes" setting.

• smtp_tls_per_site: a combined (NONE + MAY) lookup result for (hostname and next-hop destination) produces counter-intuitive results for different main.cf settings. TLS is enabled with " smtp_tls_enforce_peername = no", but it is disabled when both " smtp_enforce_tls = yes" and " smtp_tls_enforce_peername = yes".

The smtp_tls_per_site limitations were removed by the end of the Postfix 2.2 support cycle.