What is this log message telling me?

I still get the same error on cron and don't know where to set the Site URI.

[error] Stop sending newsletter to avoid broken links / SPAM. Site URI not specified.

Can someone explain, please.

This is how I do it now via crontab -e. Resolves my issue.

*/15 * * * * /usr/local/bin/drush -r /var/www/drupal/web core-cron --quiet --uri=my.website.name.uk

I get this same error even when i just run drush cron manually.

I thought it needed a base_url in settings.php but that was removed in drupal 8

Re @sphism : I supply the uri in the drush alias.

See the following example for the alias (balive) of our live Drupal site which is in drush/sites/balive.site.yml of the working directory where I invoke drush @balive cr.

balive:
  host: "${env.LIVESITE}"
  ssh:
    tty: 0
  root: /var/www/drupal/web
  uri: "https://${env.LIVESITE}"
  user: webadmin

where we also have export LIVESITE="our.live.site.uk" previously sourced from a script in our working directory.

I wonder whether this is 100% necessary .... but it has evolved over the years. And it works for me.

BTW, in ~/.ssh/config I have something like:

Host webadmin
     User webadmin
     Hostname our.live.site.uk
     PreferredAuthentications publickey
     IdentityFile ~/.ssh/oursite_rsa
     IdentitiesOnly yes