Earlier quoted context omitted.
I am ashamed to admit that I have no idea how email works. Is there a dumb down explanation of what are the moving parts and how you can achieve that sweet spot?
You send your email through a client. That client then sends (transfers / SMTPs) that email through an MTA either bundled with it or provided by your mail server. The MTA parses the message, figures out who it needs to go to (To, CC, BCC headers), figures out what servers receives mail for those recipients, and then transfers (SMTPs) it to the server. What OP is referring to is that the MTA essentially does a DNS loo…
That may happen, but not for the purpose you stated. MTA just uses addresses you told it to use in the SMTP dialog. It doesn't use addresses from the message. In fact the addresses in the message may be totally different.