Log Message:
Update postfix to 2.11.6, security release.

With all supported Postfix releases, the default settings have been
updated so that they no longer enable export-grade ciphers, and no
longer enable the SSLv2 and SSLv3 protocols. These ciphers and
protocols have little if any legitimate use today, and have instead
become a vehicle for downgrade attacks. There are no other code
changes.

Postfix documentation has been updated to reflect the new default
settings and their rationale; the RELEASE_NOTES give suggestions
for how to enable the old ciphers and protocols if your infrastructure
requires them.

Finally, abandoning deprecated ciphers and protocols does not really
improve TLS security without measures to better authenticate remote
servers. Secure DNS and TLSA are steps in that direction.