Description of problem:

When installing the exim package from EPEL 10 repository on AlmaLinux 10 (or similar RHEL 10 derivative), the RPM installation process displays warnings related to missing user/group, and consequently, the critical /var/spool/exim directories are created with incorrect ownership (root:root) instead of the required exim:exim.

This is a regression introduced by the change in the package's user/group creation method from the traditional %pre scriptlet (useradd/groupadd) in EPEL 9 to using the systemd-sysusers configuration file in EPEL 10.

Version-Release number of selected component (if applicable):

exim-4.98.2-2.el10_1.x86_64

How reproducible:


Steps to Reproduce:

1. Ensure EPEL 10 repository is enabled on a clean AlmaLinux 10 system

2. Install the package:

```bash
sudo dnf -d 9 install exim
```

Actual results:
1. During the package installation phase, the RPM utility prints multiple warnings:

```bash
...
Installing       : exim-4.98.2-2.el10_1.x86_64  
warning: user exim does not exist - using root
warning: group exim does not exist - using root
[... repeated warnings ...]
...
Running scriptlet: exim-4.98.2-2.el10_1.x86_64
Creating group 'exim' with GID 93.
Creating user 'exim' (n/a) with UID 93 and GID 93.
```

2. The resulting ownership of the spool directories is incorrect (root:root):

```bash
ls -la /var/spool/exim/
# Expected: drwxr-x--- 5 exim exim
# Actual:   drwxr-x--- 5 root root 43 Dec 11 05:05 .
```

3. The MTA fails to function correctly (e.g., cannot write queue files) due to incorrect permissions.


Expected results:

The spool directory /var/spool/exim/ and its subdirectories (db, input, msglog) should be owned by exim:exim, as defined by the %defattr directive in the spec file:

```bash
%defattr(-,exim,exim)
%dir %{_var}/spool/exim
%dir %{_var}/spool/exim/db
# ...
```

Additional info:
The issue is a timing problem inherent to the systemd-sysusers method: the file ownership application (via %defattr) occurs before the exim user and group are fully created and recognized by the system at the time of file extraction.

To resolve this, the package maintainer should reintroduce an explicit ownership change in a post-installation scriptlet (%post), after the exim user and group have been ensured to exist: