Another thing I am pondering is how best to debug the SMTP connection. tcpdump shows me the dns lookup, and a connection to the correct port (465) but the server itself (exim) gives me a "TLS error on connection from <host/ip> SSL_accept: TCP connection closed by peer", while fleetdm pops up a "sending mail: could not dial smtp host: SMTP connection error" which suggests that the "dial deadline" has been reached.
6 months ago
What do you get if you
curl -vv smtp://<host>:<port>
from the host running your Fleet server?Does your server perhaps try to negotiate a TLS connection immediately rather than using STARTTLS?