Can't get smtp platform to work

Configuration
1

Running HA in Docker with host networking.

Want to send email messages when some events occur, so I created a new notification using the smtp platform, as described here.

The relevant part of configuration.yaml looks like this:

notify:
  - name: "email_admin"
    platform: smtp
    server: <redacted>
    sender: home_assistant@<redacted>
    recipient: admin@<redacted>

When HA starts up, I get the following in the log:

ERROR (MainThread) [homeassistant.components.notify] Error setting up platform smtp

… traceback …

OSError: [Errno 113] Host is unreachable

I can send mail to to the SMTP host from the HA host command line with the mail command.

I also have the Ping (ICMP) integration set up to monitor the SMTP host and that shows the host as being connected.

The SMTP host is on the same network as the HA host.

Any ideas?

MV

2

I had to specify more

  - name: NOTIFIER_MAIL
    platform: smtp
    server: relay.xxx.xxx
    port: 25
    timeout: 60
    sender: xxx
    encryption: starttls
    recipient:
      - xxx
    sender_name: HomeAssistant
    debug: True
3

Yes, that was the problem.
The default values for “port” and “encryption” should have worked, but apparently my SMTP server doesn’t like that combination.
And the “host not reachable” message sent me looking for the problem in the wrong direction.