Should you see any TLS/SSL related errors in Exim's logs on a DirectAdmin server (on a recipient's side) we have a possible explanation and fix.
Here are two examples of such errors:
(SSL_accept (TLSv1)): error:14209102:SSL routines:tls_early_post_process_client_hello:unsupported protocol
(SSL_accept): error:1417A0C1:SSL routines:tls_post_process_client_hello:no shared cipher
The reason might still be the same.
A sending server or software is using too old and insecure SSL/TLS ciphers or protocol.
Check the article:
for a possible fix on your server's side.