So I set up a mail server on my VPS with cyberpanel and I can send emails manually through rainloop. I also have a program based on the lettre crate for Rust which runs perfectly fine on my own devices and correctly sends emails out through code. However when I try to run the program on my VPS, I get the following messages in my syslog.
globalfun postfix/smtps/smtpd[24656]: connect from localhost[::1]
globalfun postfix/smtps/smtpd[24656]: SSL_accept error from localhost[::1]: -1
globalfun postfix/smtps/smtpd[24656]: warning TLS library problem: error 14094418:SSL routines:ssl3_resl3_read_bytes: tlsv1 alert unknown ca:../ssl/rec/layer_s3.c:1543:SSL alert number 48:
globalfun postfix/smtps/smtpd[24656]: lost connection after CONNECT from localhost[::1]
globalfun postfix/smtps/smtpd[24656]: disconnect from localhost[::1] commands=0/0
I don't really understand why I can't send out emails through my program but it seems to have something to do with SSL. For reference, I have two servers on the same domain - one for my website which has an SSL installed through Let's Encrypt and another for the mail server which doesn't have SSL on it. That said, I don't think that's the issue as I can send emails through the mail server manually completely fine. Does anyone have any ideas as to what's wrong? Thanks in advance.
globalfun postfix/smtps/smtpd[24656]: warning TLS library problem: error 14094418:SSL routines:ssl3_resl3_read_bytes: tlsv1 alert unknown ca:../ssl/rec/layer_s3.c:1543:SSL alert number 48:
Your client refuses to connect to your mail server since it does not trust the CA which issued the mail servers certificate. It notifies the server about this problem by sending a unknown ca TLS alert.
There can be various reasons for this. Typically it is either the use of a CA which is not trusted by the client which need to be fixed at the client (trust this CA) or at the server (use a certificate from a CA trusted by the client). Or the root CA is actually trusted but the server is not sending the intermediate certificates needed by the client to build the trust chain to this trusted root CA. This need to be fixed at the server.