I'm doing internet servers for like 30 years now. The last three years I went back into operations and working with all the new infrastructure wonders. Feels really great. From time to time I am doing work on our mailserver that is used as a relay for customer machines. The mail queue is always a place to have a look at for things going wrong with mails.
When checking on some of the destination domains that are currently not reachable, I see a lot of domains that have no MX records set at all. My knowledge is: if you want to be reliably reachable by mail add at least two MX records of mail servers that will be able to receive mail for that domain. One master and one fall back machine. Having no MX record at all the mail server will fall back to retrieving the IP Adress of the destination mail server via the A record of its domain.
The domains in question are from businesses that are real no spam hosts or such.
These sites are misconfigured. Roughly 15 years ago such configuration would be a sure pointer to an IT department running on windows without a clue about the internet.
Did I miss anything important changes in mail configuration or is the mail misconfiguration just on the rise?