Relay email for some addresses, forward for others with Postfix

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I administer a domain (let's say example.com) for a client who uses an Exchange server at an external service provider for email. So I made the MX record point to the Exchange server, let's say mail.provider.com. Now I want email to a single address me@example.com forwarded to my own email account me@me.com. Unfortunately, the service provider told me that they're not able to do this for some reason.

Since I have control over the MX record, my idea is to make it point to my own server running Postfix and

  • forward email to me@example.com to me@me.com
  • relay all other addresses to mail.provider.com

The solution I came up with is to add the domain to relay_domains and set up a Postfix transport map

relay_domains = example.com
transport_maps = hash:/etc/postfix/transport

that contains

me@example.com    virtual:
example.com       :[mail.provider.com]
.example.com      :[mail.provider.com]

Then add an entry to the virtual alias map

me@example.com    me@me.com

I think this should work but it looks a bit ugly. Would this work at all? Is there a nicer solution?

Best Answer

Instead putting me@example.com in transport_maps, you can skip that step and use virtual_alias_maps directly.

# transport maps
example.com       :[mail.provider.com]
.example.com      :[mail.provider.com]

# virtual alias maps
me@example.com    me@me.com

Virtual alias maps is special mapping in postfix that overrides email aliasing regardless their domain class. You can use it for relay_domains, local_domains, or virtual_mailbox_domains.

Beside technical point, I would also point out that your client will aware that your server sit in front of their real server. They may think that you are snooping their conversation. You should think the some implications from this method.

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