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Asked: 2024-10-02T12:59:28+05:30

How can I configure the MAIL FROM address to change based on the envelope recipient in Postfix? I want the sender’s information in the SMTP envelope to determine the MAIL FROM address that is used for outgoing emails.

I’ve been trying to figure out how to configure the MAIL FROM address in Postfix so that it actually changes depending on the envelope recipient. I feel like I’ve read through a ton of documentation and it’s all just a blur at this point.

Basically, I want to set it up so that when my email server sends out messages, the MAIL FROM address reflects the SMTP envelope sender in accordance with the recipient’s address. For example, if the email is going to userA@example.com, I’d like the MAIL FROM address to be something like userA-mail@example.com. But if the recipient is userB@example.com, then it should change to userB-mail@example.com instead.

Is there a way to manage this dynamically within Postfix? I’ve heard that using some sort of sender-dependent configurations might be the key. But the documentation I’ve come across doesn’t really explain how to do this in a clear way, and I don’t want to mess up the current configuration by diving in without a solid understanding.

I’ve thought about using transport maps or maybe even rewriting the envelope sender address, but I’m not quite sure where to begin. If someone has experience with this or if you’ve gone through a similar process, could you please share the steps you took? Or maybe some example configurations that would help clarify things?

I’m also worried about the potential impact on deliverability or any spam filters that could get triggered with this approach. Should I be concerned about that?

Honestly, I just want to ensure that everything works smoothly for both my users and our mail reputation. Any thoughts or insights would be hugely appreciated! Thanks!

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    2 Answers

    1. To set up Postfix so that the MAIL FROM address changes based on the envelope recipient, you can use sender-dependent relayhost and sender-dependent address rewriting. Here’s a basic way to get you started:

      1. Enable Sender Dependent Address Rewriting

      You can do this by editing your main Postfix configuration file, usually located at /etc/postfix/main.cf. Add these lines:

      sender_dependent_relayhost_maps = hash:/etc/postfix/sender_relay

      2. Create the Relay Map

      Next, create the relay map file /etc/postfix/sender_relay. Here you will specify the mapping of each user to its custom MAIL FROM address:

      userA@example.com    userA-mail@example.com
userB@example.com    userB-mail@example.com

      3. Compile the Map

      After editing the sender_relay file, you’ll need to compile this into a format Postfix can read. Run:

      postmap /etc/postfix/sender_relay

      4. Update main.cf for Address Rewriting

      Add these lines to your main.cf to handle address rewriting:

      smtp_generic_maps = hash:/etc/postfix/generic

      5. Create the Generic Map

      Now create /etc/postfix/generic and add similar mappings:

      userA@example.com    userA-mail@example.com
userB@example.com    userB-mail@example.com

      6. Compile the Generic Map

      Just like before, run:

      postmap /etc/postfix/generic

      7. Reload Postfix

      Finally, apply your changes by reloading Postfix:

      systemctl reload postfix

      Concerns about Deliverability

      Changing the MAIL FROM address like this can potentially impact deliverability. Make sure that the new addresses are properly set up and authenticated (like SPF and DKIM) to avoid being flagged as spam. Always test these setups by sending emails to different providers to check if it lands in the inbox or spam folder.

      This should get you going in the right direction! Just ensure your users are aware of the change and test thoroughly.

    2. To configure the MAIL FROM address dynamically in Postfix based on the recipient’s address, you can use the sender-dependent configurations feature, which allows you to define different outbound sender addresses depending on various criteria. Start by creating a transport map, which you will use to specify the routing logic and rewrite the MAIL FROM address. You can define a transport map by creating a new file, for instance /etc/postfix/transport, with entries such as:

      userA@example.com userA-mail@example.com
userB@example.com userB-mail@example.com

      Once you’ve set up your transport file, you’ll have to tell Postfix to use it by adding configurations to /etc/postfix/main.cf:

      transport_maps = hash:/etc/postfix/transport
smtp_generic_maps = hash:/etc/postfix/generic

      Then, don’t forget to compile the transport map using postmap /etc/postfix/transport and restart Postfix. Additionally, you can use generic maps to rewrite user login addresses to your desired MAIL FROM format. As for deliverability concerns, make sure that the domain you are using in your MAIL FROM address is properly configured with SPF, DKIM, and DMARC, as these authentication methods significantly improve your chances of avoiding spam filters. Always thoroughly test your setup in a staging environment to prevent issues in production.