I, too, have referred to the debian.org document to which you link. I have spent more time linking to https://samhobbs.co.uk/2013/12/raspberry-pi-email-server-part-1-postfix, which is a bit dated. I have written my own guide which works for me. If you (or anyone else) /msg me an email address, I'll gladly send you a copy with a few caveats.

Q1) Is gitlab a better source host than github (or google)?

How long is a piece of string? Everything is a compromise and it must depend on how those compromises fit your use case. If you are trying to build a library of code for a CV, Github is where people will start looking. I run my own server, turned off most of the time, using gogs https://gogs.io/, which ISTR is available on apt.

Q2) How do I silence the mail queue?

If by "silence" you mean "purge obsolete entries", sudo postsuper -d ALL is another option.

"It seemed to me I needed "someone" dedicated to being the mailchimp, who is not in the sudo group" is not my experience.

Q3) Should I substitute sammy for root in the above?

I'm not sure. I have a dedicated Pi running postfix, so root and any "boss" user of postfix are essentially the same, so I haven't had to work through your problem.

3.1 - Unattended upgrades

Raspbian (or whatever it's called now) comes with this set up by default. The file contains lots of comments, removed below:

dr@mail:~ $ cat /etc/apt/apt.conf.d/50unattended-upgrades
Unattended-Upgrade::Origins-Pattern {
        "origin=Debian,codename=${distro_codename},label=Debian-Securi
+ty";
};
Unattended-Upgrade::Package-Blacklist {
};
[download]

3.2 /etc/hosts

dr@mail:~ $ cat /etc/hosts
127.0.0.1       localhost mail
::1             localhost ip6-localhost ip6-loopback
ff02::1         ip6-allnodes
ff02::2         ip6-allrouters

127.0.1.1       mail
[download]

Q4) What does /etc/aliases look like on a working install

dr@mail:~ $ sudo cat /etc/aliases
[sudo] password for dr:
# See man 5 aliases for format
#postmaster:    root
postmaster:    dr
root:          dr
[download]

Regards,

John Davies

Thx, John, your examples are very helpful. I've taken some more steps to get squared away, added a little architecture. So I see postsuper is how to deal with mailq:

 
wilma@mail:~$ sudo -i
[sudo] password for wilma: 
root@mail:~# which postsuper
/usr/sbin/postsuper
root@mail:~# man postsuper
root@mail:~# mailq
...
18AEEFCBE8     2970 Mon Oct 17 20:14:02  MAILER-DAEMON
(Host or domain name not found. Name service error for name=merrillpje
+nsen.com type=MX: Host not found, try again)
                                         root@merrillpjensen.com

-- 19 Kbytes in 10 Requests.
root@mail:~#  postsuper -d 18AEEFCBE8
postsuper: 18AEEFCBE8: removed
postsuper: Deleted: 1 message
root@mail:~# mailq
-Queue ID-  --Size-- ----Arrival Time---- -Sender/Recipient-------
...
6105EFCBD7     2970 Fri Oct 14 20:16:08  MAILER-DAEMON
(Host or domain name not found. Name service error for name=merrillpje
+nsen.com type=MX: Host not found, try again)
                                         root@merrillpjensen.com

-- 16 Kbytes in 9 Requests.
root@mail:~# postsuper -d ALL
postsuper: Deleted: 9 messages
root@mail:~# mailq
Mail queue is empty
root@mail:~#
[download]

I'm glad to be able to do that. I wondered upthread aloud whether these wraiths would live forever. Apparently, these 10 didn't.

aliases in etc

I think I'm getting closer to the mark here.

root@mail:~# vi /etc/hosts
root@mail:~# cat /etc/hosts
...
127.0.1.1 mail.merrillpjensen.com mail 
127.0.0.1 localhost
192.168.12.1 mail.merrillpjensen.com mail
...
[download]

I don't know which numbers on the left a person can use, and I'm taking my best 2 guesses with:

127.0.1.1 mail.merrillpjensen.com mail 
192.168.12.1 mail.merrillpjensen.com mail
[download]

, figuring that one or the either might be right, given other settings. We shall see.

Moving on to /etc/alias, I tried to imitate davies' scheme:

root@mail:~# vi /etc/aliases
root@mail:~# cat /etc/aliases
# See man 5 aliases for format
postmaster:    sammy
root: sammy
root@mail:~# newaliases
root@mail:~# cat /etc/aliases
# See man 5 aliases for format
postmaster:    sammy
root: sammy
[download]

Looking at the mx records

So, I think this is where I have a glitch, and you have to start with your service provider, which, in my case is Digital Ocean. I've had the account for long enough that port 25 isn't blocked, which we determined at the end of the last thread. (Which reminds me, what's stevieb up to? If I'm OT, let's have some quality threaddrift.)

This screenshot shows my DNS records as they appear on my account with DO. In creating this MX record, I found myself unable to enter anything other than the @ character for the hostname, which outputs it like you see.

Q1) Is it plausibly correct?

I think write-ups are good for people. I was about to lay out all the host commands I had spewed out that hadn't worked:

, and then I hit paydirt looking at my own data during the writeup:

root@mail:~# host -t MX www.merrillpjensen.com
www.merrillpjensen.com mail is handled by 5 mail.merrillpjensen.com.
root@mail:~#
[download]

Q2) Is it plausibly correct? Here is what the hostname command reveals:

root@mail:~# man hostname
root@mail:~# hostname -f
mail.merrillpjensen.com
root@mail:~# hostname -d
merrillpjensen.com
root@mail:~#
[download]

other architecture

I checked the architecture for /etc/bash.bashrc:

root@mail:~# cat /etc/bash.bashrc
# System-wide .bashrc file for interactive bash(1) shells.
...
export MAIL=~/Maildir
root@mail:~#
[download]

This looks right to me. Changed this:

postconf -e "mydestination = mail.merrillpjensen.com, localhost.locald
+omain, localhost"
[download]

Q3) Is it plausibly correct?

I thought there was a utility to add the appropriate subdirectories of Maildir, but I couldn't hook it up, so I did it on the command line:

cd /home/sammy/Maildir/
mkdir new cur temp
[download]

I have tried everything but the kitchen sink with telnet, I still don't have anything getting to sammy:

root@mail:/home/sammy/Maildir# telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 mail ESMTP Postfix (Ubuntu)
mail from:<root@www.merrillpjensen.com>
rcpt to:<sammy@www.merrillpjensen.com>
data
To: sammy@www.merrillpjensen.com
From: root@www.merrillpjensen
Subject: Hey my first email
This is my first email on debian postfix after installing configuring 
+it.
It was easy. (like hell)
Sounds good!250 2.1.0 Ok
250 2.1.5 Ok
354 End data with <CR><LF>.<CR><LF>
.
quit
.
250 2.0.0 Ok: queued as 8BC30FCD5B
quit
221 2.0.0 Bye
Connection closed by foreign host.
root@mail:/home/sammy/Maildir# ll -R
.:
total 20
drwxrwx--x 5 sammy mymail 4096 Oct 18 05:27 ./
drwxr-x--- 3 sammy sammy  4096 May 18 22:18 ../
drwxr-xr-x 2 sammy mymail 4096 Oct 18 05:27 cur/
drwxr-xr-x 2 sammy mymail 4096 Oct 18 05:27 new/
drwxr-xr-x 2 sammy mymail 4096 Oct 18 05:27 temp/

./cur:
total 8
drwxr-xr-x 2 sammy mymail 4096 Oct 18 05:27 ./
drwxrwx--x 5 sammy mymail 4096 Oct 18 05:27 ../

./new:
total 8
drwxr-xr-x 2 sammy mymail 4096 Oct 18 05:27 ./
drwxrwx--x 5 sammy mymail 4096 Oct 18 05:27 ../

./temp:
total 8
drwxr-xr-x 2 sammy mymail 4096 Oct 18 05:27 ./
drwxrwx--x 5 sammy mymail 4096 Oct 18 05:27 ../
root@mail:/home/sammy/Maildir# mailq
-Queue ID-  --Size-- ----Arrival Time---- -Sender/Recipient-------
8BC30FCD5B*     479 Wed Oct 19 06:33:56  root@www.merrillpjensen.com
                                         sammy@www.merrillpjensen.com

7AFE9FCD5F      966 Tue Oct 18 20:00:01  root@merrillpjensen.com
(Host or domain name not found. Name service error for name=merrillpje
+nsen.com type=MX: Host not found, try again)
                                         root@merrillpjensen.com

0AB56FCD57      460 Tue Oct 18 05:50:04  root@merrillpjensen.com
(Host or domain name not found. Name service error for name=merrillpje
+nsen.com type=MX: Host not found, try again)
                                         sammy@merrillpjensen.com

-- 1 Kbytes in 3 Requests.
root@mail:/home/sammy/Maildir#
[download]

That last try looked particularly wrong with the www in it, but I have previous versions failing without that. I wouldn't say that I have a strong handle on fqdn:

   THE FQDN
       The  FQDN  (Fully Qualified Domain Name) of the system is the n
+ame that
       the resolver(3) returns for the host name, such as, ursula.exam
+ple.com.
       It  is  usually  the hostname followed by the DNS domain name (
+the part
       after the first dot).  You can check the FQDN using hostname --
+fqdn  or
       the domain name using dnsdomainname.

       You cannot change the FQDN with hostname or dnsdomainname.

       The  recommended  method of setting the FQDN is to make the hos
+tname be
       an alias for the fully qualified name using /etc/hosts,  DNS,  
+or  NIS.
       For  example,  if  the  hostname was "ursula", one might have a
+ line in
       /etc/hosts which reads

              127.0.1.1    ursula.example.com ursula

       Technically: The FQDN is the name getaddrinfo(3) returns for  t
+he  host
       name returned by gethostname(2).  The DNS domain name is the pa
+rt after
       the first dot.

       Therefore it depends on the configuration of the resolver  (usu
+ally  in
       /etc/host.conf) how you can change it. Usually the hosts file i
+s parsed
       before DNS or NIS,  so  it  is  most  common  to  change  the  
+FQDN  in
       /etc/hosts.
[download]

I was hoping to break through with this effort, but I seem to have come up short again.

Q1) Is gitlab a better source host than github (or google)?

Yes, because it isn't owned by a malignant corporation and because it's open source.

Q2) How do I silence the mail queue?

You don't want to silence it, you just want to remove the messages which are stuck in the queue and will never be delivered. qtool.pl is probably best for this.

Q3) Should I substitute sammy for root in the above?

You could if someone is going to be sure to read sammy's email. So long as someone is getting and reading the postmaster emails it can be any user.

Q4) What does /etc/aliases look like on a working install?

I'm not sure what you mean by this. The format is as described in the man page. Are you asking for someone to post an in-production aliases file?