systemd (OnFailure) using ssmtp with gmail can't send mail

Question

Some important service:

[Unit]
...
OnFailure=status-email@%n.service

status-email@.service:

[Unit]
Description=status email for %i to user

[Service]
Type=oneshot
ExecStart=/usr/local/bin/systemd-email.sh <recipient> %i
User=root
Group=systemd-journal

[Install]
WantedBy=multi-user.target

I'm getting error systemd-email.sh[117310]: ssmtp: Cannot open smtp.gmail.com:587

I can send mail manually ./systemd-email.sh $RECIPIENT $SERVICE_NAME

It's also working as cronjob.

My /etc/ssmtp/ssmtp.conf:

root=<gmail address>
mailhub=smtp.gmail.com:465
FromLineOverride=YES
AuthUser=<gmail address>
AuthPass=<password>
UseTLS=YES

Why cron can send mail in this setup but systemd cannot?

Answer 1

Per the comments, the problem was an incorrectly configured port number somewhere else. Please consider deleting this question, as the main thing it brings to the community and the site/network is "Why you should do a detailed search/research, troubleshooting, and/or diagnostics to exhaust all avenues of resolving the issue on your own."

The only thing I would add to help other/future users is application of various template files and configuration files (setting an environment variable to the correct value, then using it in other files) to ensure a single change propagates to all sub-ordinate configuration files.