At package doesn't include sendmail package dependency

[Saverio Miroddi]

The `at` program uses the local mail in order to report errors, specifically, it requires the `sendmail` binary.

Without `sendmail`, any error during a job execution is reported in the syslog with a very confusing reference to a missing "mail" program.

I suppose that error diagnosis is a requirement in job scheduling, therefore, the `sendmail` package should be required by the `at` package.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: at (not installed)
ProcVersionSignature: Ubuntu 5.4.0-39.43-generic 5.4.41
Uname: Linux 5.4.0-39-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.3
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: MATE
Date: Wed Dec 30 17:41:51 2020
InstallationDate: Installed on 2020-07-01 (182 days ago)
InstallationMedia: Ubuntu-MATE 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
SourcePackage: at
UpgradeStatus: No upgrade log present (probably fresh install)

[Paride Legovini (paride)]

Hi Saverio and thanks for this bug report.

This is intentional: `at` is currently a dependency of the ubuntu-server metapackage, however we wanted to avoid installing a full MTA by default in Ubuntu Server as a transitional dependency of `at` (and more in general we wanted to avoid installing a full MTA by default). For this reason the `at` package has `default-mta` as a Suggests instead of Recommends.

At the moment we are in the process of dropping the ubuntu-server dependency on `at`. Once this is done we'll consider making `at` a sync from Debian, thus bringing back the Recommends: default-mta. For the moment just install it manually.

[Paride Legovini (paride)]

An update on this. Now that at is in universe we can safely make it a sync from Debian. There are currently three changes in the Ubuntu delta:

(1) Suggest an MTA rather than Recommending one.
    This can be dropped, and dropping it will fix this very bug.
(2) d/patches: add 03-do-not-drop-seconds.patch (cherry-pick).
    Fixed in Debian experimental which packages a newer upstream version.
(3) d/t/{control, basic-usage}: Add DEP8 test
    Utkarsh will submit these to Salsa for inclusion. Ideally we'll wait
    for them to be included in Debian before proceeding with the sync,
    so there will be no "downgrade" (removed tests) in Ubuntu.

Debian tracking the inclusion of the autopkgtests: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=985421

[Paride Legovini (paride)]

MR to add the Ubuntu autopkgtests to the Debian package:

https://salsa.debian.org/debian/at/-/merge_requests/26

Once that's merged and released to Debian I think we can make the package a sync.

[Paride Legovini (paride)]

Fix Released by 3.2.4-1, thanks Utkarsh for the sync.