Add tutorial: Setting Up Proxmox Mail Gateway as a VM on Proxmox VE

[ikrsdo]

I have read and understood the Contributor's Certificate of Origin available at the end of
https://raw.githubusercontent.com/hetzneronline/community-content/master/tutorial-template.md
and I hereby certify that I meet the contribution criteria described in it.
Signed-off-by: Kürşad Ölmez kursad.olmez@gmail.com

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This tutorial covers installing Proxmox Mail Gateway as a VM on a Proxmox VE dedicated
server, configured as the primary mail-receiving gateway for a domain. It walks through
the core Mail Proxy settings (relaying, relay domains, transports, networks, TLS, DKIM),
SMTP-level hardening (HELO/SPF/receiver verification), the no-subscription repository,
Spam Detector and Virus Detector engine configuration, extending ClamAV with third-party
signature feeds, and the DNS records needed to go live. No existing tutorial covers PMG.

[svenja11]

Thank you for your contribution @ikrsdo. I started testing your tutorial and noticed a view things. Please update the tutorial accordingly.

• In step 3, please be more precise how to set up the network interface. If an additional IP needs to be ordered, please add a note in the prerequisites as well. Please also add commands how to get relevant information.

• In step 3, qm set 200 --ide2 none itself didn't work for me. Here's what I had to run:

  qm stop 200
  qm set 200 --ide2 none
  qm set 200 --boot order=scsi0
  qm start 200

• Step 4 failed for me, meaning the web UI wasn't accessible for me. I assume I made a mistake in step 3. I had to resort to this to continue testing:

  ssh -L 8080:<pmg_ip>:8006 root@<proxmox-server-ip>

  In my local browser:

  https://localhost:8080/
  

• In step 5, please mention that this need to be run on the mail gateway vm. Either via the Proxmox UI at <proxmox-server-ip>:8006 (Datacenter → your node → 200 (mail-gateway) → Console) or via:

  ssh root@<proxmox_server>
  root@pve:~# ssh root@<pmg_ip>

Once this is resolved, I will continue testing.