Currently client email is submitted via ssmtp (port 465).  This has been
deprecated for years.  The correct way to submit email is via
submission (port 587).

This patch adds port 587 as a second and the default way of submitting
email for delivery.  Port 465 remains open for backwards compatibility
with existing clients.

This allows the `recipient_delimiter` setting in etc_postfix_main.cf.j2
to function as intended.

Fixes: #121

These are the changes necessary to enable Roundcube's manage sieve plugin to mange server-side sieve filters.

Signed-off-by: PajamaSoft <support@pajamasoft.com>