> We can see helpfile and statistics file go into etc/mail, then sendmailgoes
into sbin, smrsh is missing in sbin.

Fixed.

In addition to Léo Le Bouter's comments, I suggest either omitting or
> amending this part. A Maildir is where the user's emails will be kept,
> but it cannot be stored in the build output, because that directory will
> be immutable after the build is complete.

 >

> What is the default?
>

`/etc/mail` is the default it seems. I modified the patch to use
`$out/var/spool/mail` instead. `/var/spool/mail` is where I would like to
put it on a conventional linux distribution. But I don't know if MAILDIR
means "where the user's mail will be kept" in this context because when I
do that I end up with the following file tree:


$ tree /gnu/store/05wxmp6m3pfg5d2jrwbx4rx5p3nxyyvc-sendmail-8.15.2
> /gnu/store/05wxmp6m3pfg5d2jrwbx4rx5p3nxyyvc-sendmail-8.15.2
> ├── bin
> │   ├── hoststat ->
> /gnu/store/05wxmp6m3pfg5d2jrwbx4rx5p3nxyyvc-sendmail-8.15.2/sbin/sendmail
> │   ├── mailq ->
> /gnu/store/05wxmp6m3pfg5d2jrwbx4rx5p3nxyyvc-sendmail-8.15.2/sbin/sendmail
> │   ├── newaliases ->
> /gnu/store/05wxmp6m3pfg5d2jrwbx4rx5p3nxyyvc-sendmail-8.15.2/sbin/sendmail
> │   ├── purgestat ->
> /gnu/store/05wxmp6m3pfg5d2jrwbx4rx5p3nxyyvc-sendmail-8.15.2/sbin/sendmail
> │   └── vacation
> ├── etc
> │   └── mail
> │       ├── helpfile
> │       └── statistics
> ├── libexec
> │   └── smrsh
> ├── sbin
> │   ├── editmap
> │   ├── mailstats
> │   ├── makemap
> │   ├── praliases
> │   └── sendmail
> ├── share
> │   └── doc
> │       └── sendmail-8.15.2
> │           └── LICENSE
> └── var
>     └── spool
>         └── mail
>             ├── sendmail.cf
>             └── submit.cf
>

with config files for sendmail in `$out/var/spool/mail`.