[FEATURE] Add advanced records to DNS for email (SRV)

[Oceanwatcher]

There are a number of records that should be added to the DNS to help email clients figure out the server configuration. There are other records that can be added for other services, but the following list should be a minimum:

# Name              Type       Priority Weight Port    Value
_autodiscover._tcp  IN SRV     0        1      443      mail.example.org.
_imap._tcp          IN SRV     0        1      143      mail.example.org.
_imaps._tcp         IN SRV     0        1      993      mail.example.org.
_pop3._tcp          IN SRV     0        1      110      mail.example.org.
_pop3s._tcp         IN SRV     0        1      995      mail.example.org.
_smtps._tcp         IN SRV     0        1      465      mail.example.org.
_submission._tcp    IN SRV     0        1      587      mail.example.org.