ThinLinc depends on the sendmail binary for emailing license notifications. Since bug 7716, we use the `default-mta` package as the provider for this on Debian-based systems. This gives us the sendmail binary, but also installs postfix, which ends up running as an (unwanted) SMTP server on port 25. We can avoid this by selecting `esmtp-run` instead, which provides sendmail without installing an SMTP server, and is more consistent with our approach for other distros.
This seems to be the recommended way programs should solve the issue of needing to send mail. Debian's discussions here show that applications should depend on default-mta if they need to send email: https://wiki.debian.org/Debate/DefaultMTA https://lists.debian.org/debian-devel/2007/10/msg00717.html We can also see that this is how cron is packaged: https://packages.ubuntu.com/oracular/cron https://salsa.debian.org/debian/cron/-/blob/master/debian/control?ref_type=heads#L31 I don't yet see a compelling reason why we should override their decision and behave different from packages included in the distribution. This is also similar to what we do for other distributions. For SUSE and Red Hat/Fedora, we tell the package manager we want /usr/sbin/sendmail and let it decide which package is appropriate for that. Let's keep doing what everyone else is doing. It should give us the most robust and least surprising behaviour.
