I'm just learning about DNS records, and it seems that MX records are redundant.
My understanding of MX records is as such: If I ask my DNS about an email address, then my DNS will look at a MX record to determine what IP to send my mail to.
But that doesn't seem to be any different than an A record. If I ask my DNS about a domain, then my DNS will look at an A record to determine what IP to send my queries to.
If I submitted a POST request to a URL, with a file as part of the query, then I could accomplish what email does without the need for a MX record. (And because we're all using mail applications anyway, this doesn't seem harder on the end user). However, I have no idea what this difference means to the network engineer, or DNS admin. I don't even know enough to know WHO it would matter to.
So I ask: Why does mail need to have (or get to have) its own special DNS record type? Are MX records an artifact of how things used to be? What am I missing?