Add info about sendgrid relay

Update emailwiz.sh

Ubuntu can't run multiple lines without a special character, thus making the script malfunction, putting the commands on the same line solves the problem and the script can be used on Ubuntu 20.04

Fixes for custom subdomain names

Enforce TLS1.2 connections

Add extra troubleshooting points, minor readability changes

documentation changes

Make README clearer about PTR record

Fixed Tiny Grammar Error

Literally added one letter

Minor change for dovecot.conf to work on v2.3

According to the wiki (https://wiki.dovecot.org/SSL/DovecotConfiguration):

"From version 2.3, you must specify path to DH parameters file using:
ssl_dh=</path/to/dh.pem"

This actually threw an error something along the lines of: "imap-login: Error: Failed to initialize SSL"

remove smtp_tls_CAfile from postfix main.cf

Change Dovecot/Postfix definition

Technically Postfix is responsible for sending *and* receiving mail between *your server and other SMTP servers* (Mail Transfer Agents). Dovecot is only so you can view your mail in email clients on your computer instead of server, which is not really *receiving*. You can have a perfectly functional email system with no IMAP/POP server at all, you'd just have to read your email over SSH or whatever

Added instructions for setting up reverse DNS

Added instructions for setting up reverse DNS