Configuring a mail server on a local machine running Trisquel and port-forwarding through a shared server (VPS)

Has anyone set up a mail server on a home machine AND routed traffic through a VPS (to get a static IP)?

I can't get the config right. I am confused with IPs.

I started by setting up Wireguard and nftables to "port-forward through a VPS"[1].

When I check on the VPS I get this:

# nft list ruleset
table inet filter {
chain input {
type filter hook input priority filter; policy accept;
}

chain forward {
type filter hook forward priority filter; policy accept;
}

chain output {
type filter hook output priority filter; policy accept;
}
}

table ip my_nat {
chain my_prerouting {
type nat hook prerouting priority dstnat; policy accept;
ip daddr redacted_ip_address_of_vps tcp port { 25, 134, 465, 587, 993 } dnat to 192.168.69.2
}

chain my_postrouting {
type nat hook postrouting priority srcnat; policy accept;
ip saddr 192.168.69.2 masquerade
}
}

# systemctl status nftables.service
● nftables.service - nftables
Loaded: loaded (/lib/systemd/system/nftables.service; disabled; vendor preset: enabled)
Active: active (exited) since Sun 2023-11-26 14:54:20 UTC; 1 week 2 days ago
Docs: man:nft(8)
http://wiki.nftables.org
Main PID: 15479 (code=exited, status=0/SUCCESS)
CPU: 7ms

Nov 26 14:54:20 redacted_VPS_name systemd[1]: Starting nftables...
Nov 26 14:54:20 redacted_VPS_name systemd[1]: Finished nftables.

# systemctl status name at domaine
● name at domaine - WireGuard via wg-quick(8) for wg/portforward
Loaded: loaded (/lib/systemd/system/wg-quick@.service; enabled; vendor preset: enabled)
Active: active (exited) since Tue 2023-12-05 10:19:04 UTC; 5h 45min ago
Docs: man:wg-quick(8)
man:wg(8)
https://www.wireguard.com/
https://www.wireguard.com/quickstart/
https://git.zx2c4.com/wireguard-tools/about/src/man/wg-quick.8
https://git.zx2c4.com/wireguard-tools/about/src/man/wg.8
Process: 148941 ExecStart=/usr/bin/wg-quick up wg-portforward (code=exited, status=0/SUCCESS)
Main PID: 148941 (code=exited, status=0/SUCCESS)
CPU: 19ms

Dec 05 10:19:04 redacted_VPS_name wg-quick[148941]: [#] ip link add wg-portforward type wireguard
Dec 05 10:19:04 redacted_VPS_name wg-quick[148941]: [#] wg setconf wg-portforward /dev/fd/63
Dec 05 10:19:04 redacted_VPS_name wg-quick[148953]: Warning: AllowedIP has nonzero host part: 192.168.69.2/24
Dec 05 10:19:04 redacted_VPS_name wg-quick[148941]: [#] ip -4 address add 192.168.69.1/24 dev wg-portforward
Dec 05 10:19:04 redacted_VPS_name wg-quick[148941]: [#] ip link set mtu 1420 up dev wg-portforward
Dec 05 10:19:04 redacted_VPS_name wg-quick[148941]: [#] sysctl -w net.ipv4.ip_forward=1
Dec 05 10:19:04 redacted_VPS_name wg-quick[148970]: net.ipv4.ip_forward = 1
Dec 05 10:19:04 redacted_VPS_name wg-quick[148941]: [#] sysctl -w net.ipv6.conf.all.forwarding=1
Dec 05 10:19:04 redacted_VPS_name wg-quick[148972]: net.ipv6.conf.all.forwarding = 1
Dec 05 10:19:04 redacted_VPS_name systemd[1]: Finished WireGuard via wg-quick(8) for wg/portforward.

On the local machine:

systemctl status name at domaine
● name at domaine - WireGuard via wg-quick(8) for wg/portforward
Loaded: loaded (/lib/systemd/system/wg-quick@.service; enabled; vendor preset: enabled)
Active: active (exited) since Tue 2023-12-05 11:05:43 CET; 6h ago
Docs: man:wg-quick(8)
man:wg(8)
https://www.wireguard.com/
https://www.wireguard.com/quickstart/
https://git.zx2c4.com/wireguard-tools/about/src/man/wg-quick.8
https://git.zx2c4.com/wireguard-tools/about/src/man/wg.8
Main PID: 1316 (code=exited, status=0/SUCCESS)
Tasks: 0 (limit: 9405)
Memory: 0B
CGroup: /system.slice/system-wg\name at domaine

Dez 05 11:05:43 computer systemd[1]: Starting WireGuard via wg-quick(8) for wg/portforward...
Dez 05 11:05:43 computer wg-quick[1316]: [#] ip link add wg-portforward type wireguard
Dez 05 11:05:43 computer wg-quick[1316]: [#] wg setconf wg-portforward /dev/fd/63
Dez 05 11:05:43 computer wg-quick[1316]: [#] ip -4 address add 192.168.69.2/24 dev wg-portforward
Dez 05 11:05:43 computer wg-quick[1316]: [#] ip link set mtu 1420 up dev wg-portforward
Dez 05 11:05:43 computer wg-quick[1316]: [#] ip -4 route add 0.0.0.0/0 dev wg-portforward table 69
Dez 05 11:05:43 computer wg-quick[1316]: [#] ip rule add from 192.168.69.2 table 69
Dez 05 11:05:43 computer systemd[1]: Finished WireGuard via wg-quick(8) for wg/portforward.

DNS records look like this:

mail A 1800 redacted_ip_address_of_vps
@ MX 10800 10 mail.redacted_domain_name

About PTR. I tried this:

* PTR 10800 redacted_domain_name

but mail-tester.com tells me emails are sent from a domain name of my ISP, which does not agree with the above PTR setting.

Also, mail-tester.com tells me that emails are sent from my home IP (which makes sense to me since I actually send emails from this machine,) but then, a test fail because the IP address emails are sent from is not the same as the IP (that is the one of the VPS) address entered in the DNS - which I thought is correct since it is the static IP of the VPS.

If someone has done this, or know how to troubleshoot, any help would be appreciated, or a link to a tutorial which explains how to set up a home mail server AND route traffic through a VPS? All tutorials I find are about configuring a mail server *on* a VPS.

Complementary information:

I set DKIM with content of /etc/postfix/dkim/mail.txt.

SPF:

mail TXT 10800 "v=spf1 mx a:mail.redacted_domain_name -all"

DMARC:

_dmarc TXT 300 "v=DMARC1; p=reject; rua=mailto:dmarc@redacted_domain_name; fo=1"

I was inspired by https://trisquel.info/en/forum/free-email-providers-being-banned-gmail-alternatives#comment-163588 and followed https://landchad.net/mail/ so far but I don't know if the latter is a good option.

[1] https://www.whizanth.com/blog/vps-portforwarding/