rfe: lmtp for amavis and dovecot

rfe: use lmtp to send mail to amavis and final delivery to dovecot. This gives both services the ability to reply with a dsn for each recipient (improves delivery), and is a little more efficient (not much different for amavis, but dovecot saves a fork/exec for every message).

Changes required

Required config changes are quite simple, in current (eg. 3.1.6) config for postfix + dovecot to send to amavis via lmtp you simply need these in main.cf:

lmtp_data_done_timeout = 1200 lmtp_send_xforward_command = yes

Then change the amavis transport name to lmtp in the 'tag_as_*.re' files:

sed -i s/amavis/lmtp/g /etc/postfix/tag_as_*.re

The dovecot config is in /etc/dovecot/dovecot.conf:

protocols = imap pop3 lmtp <---- line #2 lmtp_rcpt_check_quota = yes <---- new

And in main.cf change virtual_transport = lmtp:unix:private/dovecot-lmtp.

You can then remove the dovecot and amavis transports in master.cf.