Been trying to read up on this but its confusing. Let me give you an example. I am just talking server to server communication here. No clients unless you want to consider one server a client.
A user sends an email. Their server does not support TLS or encryption of any kind. The receiving gateway supports opportunistic TLS. Does the email from the server to the gateway get encrypted? I can't see how if the sending server has no certificate to encrypt the email.
Reverse this now. User behind the gateway which does support TLS encryption sends an email and the same receiving server receives it. Again, is the email encrypted? The gateway has a certificate but the receiving server does not. Receiving server does not understand TLS so again no encryption, correct?
Now both have certificates and support TLS. Email gets encrypted in both directions, but is this considered MTLS because they both have certificates?
You not believe how many different ways this gets explained and they are probably all right but explained differently.
I have read most of the articles so please don't just post a link. I need someone that understand TLS and email to explain it to me.