It seems that something as critical as email for the business environment should be protected at all costs, and that too goes for making any changes to said email servers. Especially when the nature of email is that it can take up to 48 hours for any mistakes you make to a internet facing infrastructure to propagate themselves out. So knowing what you are doing is vital.
A word of warning… I’ve seen this mistake happen time and time again (and I’ve been guilty of doing it myself once as well), ALWAYS make sure that your MX records end in a “.” if you’re directing them to another domain name take the following examples for instance.
mx1.companya.com = 22.214.171.124
mx2.companya.com = 126.96.36.199
MX preference = 10, mail exhanger = mx1
MX preference = 10, mail exchanger = mx2
This example would work if mx1.companya.com and mx2.companya.com both exist and work, and is a nice neat way to maintain email flow when looking through your DNS. Any email destined for companya.com will be sent to mx1.companya.com or mx2.companya.com automatically.
MX preference = 10, mail exchanger mx1.emailprovider.com
MX preference = 10, mail exchanger mx2.emailprovider.com
Wouldn’t work! This is because if there isn’t a dot at the end of the MX record the MTA when trying to send the message will do a DNS looking for mx1.emailprovider.com.companya.com and try to delivery there.
The dot at the end of an mx record tells the MTA it is a FQDN as opposed to a host!
Example 2 – Corrected
MX preference = 10, mail exchanger mx1.emailprovider.com.
MX preference = 10, mail exchanger mx2.emailprovider.com.
This would work ok, any MTA trying to send a mail to *@companya.com would relay to the FQDN mx1.emailprovider.com. or mx2.emailprovider.com. and your email should be ok.