I have set up my Postfix to require STARTTLS, or SSL/TLS, as well as the user being authenticated if sending to other domains, or the recipient being known to my host if receiving mail.
I can connect without initial encryption like this:
telnet myserver.com 587 elho there mail from: firstname.lastname@example.org
The server responds with
530 5.7.0 Must issue a STARTTLS command first
I noticed that smtp.gmail.com has the same requirement to use TLS.
I think this is good and what I want. But how many clients/servers who will try to send mail to my domain will fail, because they can't do SSL/TLS? My certificate is signed by letsencrypt, so that shouldn't be a problem.
Asked another way, is it safe to assume that in 2022 all mail senders can do SSL/TLS?
If not, what do I have to change in my postfix configs to allow third parties to deliver mail to my server without TLS (for mails in my domains), but still require my users who want to send mail via my server to login and use STARTTLS or SSL/TLS?
A second question: I noticed that if I send the following, I get the same error, but have I just sent my password to the server effectively unencrypted across the internet, meaning I should change my password (note the connection is done with telnet, not openssl!)
telnet myserver.com 587 ehlo there AUTH PLAIN GFudEBtYaXhdhbnQuY2...doh!