Hi Bryce,

Awesome work with this MP!

As for the "make check" part, it still doesn't work for me. I've pasted the logs below.
Simplest way to reproduce is to run sbuild and then autopkgtest via:
`autopkgtest -U -s --apt-pocket=proposed -B ../*.deb -- lxd ubuntu-daily:devel`

8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<
checking for gcc... no
checking for cc... no
checking for cl.exe... no
configure: error: in `/tmp/autopkgtest.8xasIM/build.tnJ/real-tree':
configure: error: no acceptable C compiler found in $PATH
See `config.log' for more details
autopkgtest [14:31:35]: test command1: -----------------------]
autopkgtest [14:31:36]: test command1:  - - - - - - - - - - results - - - - - - - - - -
command1             FAIL non-zero exit status 1
8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<

I started to take a look at it and after installing gcc, here's where it fails[1]: https://paste.ubuntu.com/p/3hQqkD46rF/.

But I further studied the log and it shows that you also need python, python3, and build-essential packages in order to ./configure to work.

After installing those 4 packages, the next problem I hit was:
`configure: error: SSL support enabled, but OpenSSL not found`

This means, installing libssl-dev. And then there were no errors. Yay! \o/

So the final diff that I know have, looks like:
8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<
--- a/debian/tests/control
+++ b/debian/tests/control
@@ -1,5 +1,5 @@
 Test-Command: ./configure && make check
-Depends: @
+Depends: @, build-essential, gcc, libssl-dev, python, python3
 Restrictions: allow-stderr
 
 Tests: installation
8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<

With this diff applied, I now have the tests passing:

8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<
make  check-TESTS
make[3]: Entering directory '/tmp/autopkgtest.EaEic9/build.kRF/real-tree'
make[4]: Entering directory '/tmp/autopkgtest.EaEic9/build.kRF/real-tree'
PASS: t.smoke
SKIP: t.validate-xhtml10
SKIP: t.validate-xhtml
PASS: t.x509_name_match
PASS: t.realpath
PASS: t.tls-aux
=========================================================
Testsuite summary for fetchmail 6.4.16
=========================================================
# TOTAL: 6
# PASS:  4
# SKIP:  2
# XFAIL: 0
# FAIL:  0
# XPASS: 0
# ERROR: 0
=========================================================
make[4]: Leaving directory '/tmp/autopkgtest.EaEic9/build.kRF/real-tree'
make[3]: Leaving directory '/tmp/autopkgtest.EaEic9/build.kRF/real-tree'
make[2]: Leaving directory '/tmp/autopkgtest.EaEic9/build.kRF/real-tree'
Making check in po
make[2]: Entering directory '/tmp/autopkgtest.EaEic9/build.kRF/real-tree/po'
make[2]: Nothing to be done for 'check'.
make[2]: Leaving directory '/tmp/autopkgtest.EaEic9/build.kRF/real-tree/po'
make[1]: Leaving directory '/tmp/autopkgtest.EaEic9/build.kRF/real-tree'
autopkgtest [15:11:35]: test command1: -----------------------]
autopkgtest [15:11:35]: test command1:  - - - - - - - - - - results - -
command1             PASS
8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<


-----------------------------------------------

Now, onto the next test: "operation".
Running autopkgtest yields:
`operation            FAIL stderr: + POP3_SERVER=localhost`

The "stderr" part next to FAIL immediately tells me to look at the "Restrictions" and aha!
Adding Restrictions seems to be the only thing you needed! \o/


So the final diff looks like:
8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<
--- a/debian/tests/control
+++ b/debian/tests/control
@@ -1,5 +1,5 @@
 Test-Command: ./configure && make check
-Depends: @
+Depends: @, build-essential, gcc, libssl-dev, python, python3
 Restrictions: allow-stderr
 
 Tests: installation
@@ -12,4 +12,4 @@ Restrictions: needs-root, allow-stderr
 
 Tests: operation
 Depends: @, python3
-Restrictions: needs-root
+Restrictions: needs-root, allow-stderr
8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<

And the result is:
8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<
autopkgtest [15:22:38]: test operation: -----------------------]
autopkgtest [15:22:39]: test operation:  - - - - - - - - - - results - - - - - - - - - -
operation            PASS
autopkgtest [15:22:39]: @@@@@@@@@@@@@@@@@@@@ summary
command1             PASS
installation         PASS
service              PASS
operation            PASS
8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<


Yay, indeed! \o/
Hope this helps!