I spent a good chunk of time trying to figure out how to send mail from my local machine using my Dreamhost SMTP server as a smarthost. Here’s a sample setup using msmtp:
defaults
tls on
auth on
tls_trust_file /path/to/ca-certificates.crt
logfile ~/.smtp.log
account dreamhost
host smtp.dreamhost.com
port 465
tls_starttls off
from your@email.com
user your@email.com
password yoursecretpassword
account default : dreamhostThe important bit is tls_starttls off, without which will lead to a whole world of frustration.