Domain and bounce (Return-Path) isolation with dedicated IPs – is it possible in Postal?

[SaasX]

Hello,

I am currently reworking my email sending infrastructure to optimize costs. Until now, I was using one VPS per client, but due to increasing server costs, I am looking to consolidate multiple clients into a single Postal instance.

To maintain proper reputation isolation, I have implemented:

• one dedicated IP per client
• one dedicated domain per client (e.g., client1.fr)
• aligned reverse DNS
• domain-based tracking

Everything is working correctly on that side.

However, I am facing an issue with the bounce (Return-Path).
Despite configuring domains and tracking, the bounce address remains tied to the root domain of the Postal instance (e.g., domainepostal.com), instead of the client domain (e.g., user1.fr).

This creates several problems:

• lack of full alignment (SPF / DMARC)
• reputation leakage between clients
• inconsistencies in email headers

My goal is to achieve full isolation per client:

• 1 IP = 1 domain = 1 reputation
• including the Return-Path / bounce

So my question is:
Is it possible in Postal to configure a domain-specific Return-Path (e.g., psrp.client1.fr) without relying on the instance root domain (mondomaine.racine.com)?

Or is there a recommended approach to achieve this level of isolation?

Thanks in advance for your insights.

[willpower232]

Did you set up a return path domain?

If you don't want it to be a CNAME you could probably tweak the code a little but I'm not sure.

[SaasX]

Hello,

Thank you for your help on the previous topic, I was able to resolve my return-path issue thanks to your guidance. Everything is now working correctly on that side.

I still have one remaining point I’m struggling with: HELO configuration.

Currently, I’m running multiple IPs with fully independent domains and return-paths, but the HELO remains shared at the server level. I haven’t found a clean way to differentiate it per IP or per sending stream.

Do you know if there is a recommended approach or workaround to properly segment HELO in this kind of setup with Postal?

Thanks in advance for your help.

[willpower232]

Glad you figured it out.

As there is only one SMTP server process running, I don't think it is possible for the HELO to return different values as the connection probably doesn't identify how the connection was made to split the identities.

I think its value is just another config so if you were prepared to do something big and complicated with multiple IP addresses and multiple SMTP servers, I'm sure it could be possible but the result would be quite messy and I'm not sure what the benefit would be.

I'm not currently aware of it being a problem at all unless you're trying to conceal the servers underlying identity.