email@example.com --> smtp.a.com --?--> Internet --?--> pop.b.com --> firstname.lastname@example.org
On the route from sender to server, and server to receiver, encrypted connections (STARTTLS, etc) seem to get more and more common. All major freemail providers and email programs offer encryption meanwhile.
But what about the connections between/among the various email service providers? Do they use encrypted connections between their mail / relay servers?
What's the trend there? Branch inside knowledge welcome!
I am not looking for setup instructions as i.e. in #142594, but really would like to know what's the current common practice among the Internet and the dominating (free)Mail / service providers.
Or in other words: If both sender and receiver use encrypted connections, how likely is it that an email still travels through unencrypted route sections?