If you’re using msmtp to send email through Google’s SMTP Relay Service, you might get this error: “the server sent an empty reply”.
To fix, try setting a domain in your /etc/msmtprc file. For example, if you’ve configured SMTP Relay to allow email from your server’s IP with TLS and no authentication, and your Google Workspace domain is awmb.uk, your /etc/msmtp file might look like:
defaults
auth off
tls on
logfile /var/log/msmtp
domain awmb.uk
from [email protected]
account default
host smtp-relay.gmail.com
port 587