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91 lines
3.4 KiB
Markdown
91 lines
3.4 KiB
Markdown
---
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title: 'Mail Forwarding | Relay Hosts'
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---
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## Introduction
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Rather than having Postfix deliver mail directly, you can configure Postfix to send mail via another mail relay (smarthost). Examples include [Mailgun](https://www.mailgun.com/), [Sendgrid](https://sendgrid.com/) and [AWS SES](https://aws.amazon.com/ses/).
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Depending on the domain of the sender, you may want to send via a different relay, or authenticate in a different way.
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## Basic Configuration
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Basic configuration is done via environment variables:
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* `RELAY_HOST`: _default host to relay mail through, empty will disable this feature_
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* `RELAY_PORT`: _port on default relay, defaults to port 25_
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* `RELAY_USER`: _username for the default relay_
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* `RELAY_PASSWORD`: _password for the default user_
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Setting these environment variables will cause mail for all sender domains to be routed via the specified host, authenticating with the user/password combination.
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!!! warning
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For users of the previous `AWS_SES_*` variables: please update your configuration to use these new variables, no other configuration is required.
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## Advanced Configuration
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### Sender-dependent Authentication
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Sender dependent authentication is done in `config/postfix-sasl-password.cf`. You can create this file manually, or use:
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```sh
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setup.sh relay add-auth <domain> <username> [<password>]
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```
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An example configuration file looks like this:
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```txt
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@domain1.com relay_user_1:password_1
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@domain2.com relay_user_2:password_2
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```
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If there is no other configuration, this will cause Postfix to deliver email throught the relay specified in `RELAY_HOST` env variable, authenticating as `relay_user_1` when sent from `domain1.com` and authenticating as `relay_user_2` when sending from domain2.com.
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!!! note
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To activate the configuration you must either restart the container, or you can also trigger an update by modifying a mail account.
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### Sender-dependent Relay Host
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Sender dependent relay hosts are configured in `config/postfix-relaymap.cf`. You can create this file manually, or use:
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```sh
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setup.sh relay add-domain <domain> <host> [<port>]
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```
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An example configuration file looks like this:
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```txt
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@domain1.com [relay1.org]:587
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@domain2.com [relay2.org]:2525
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```
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Combined with the previous configuration in `config/postfix-sasl-password.cf`, this will cause Postfix to deliver mail sent from domain1.com via `relay1.org:587`, authenticating as `relay_user_1`, and mail sent from domain2.com via `relay2.org:2525` authenticating as `relay_user_2`.
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!!! note
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You still have to define `RELAY_HOST` to activate the feature
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### Excluding Sender Domains
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If you want mail sent from some domains to be delivered directly, you can exclude them from being delivered via the default relay by adding them to `config/postfix-relaymap.cf` with no destination. You can also do this via:
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```sh
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setup.sh relay exclude-domain <domain>
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```
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Extending the configuration file from above:
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```txt
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@domain1.com [relay1.org]:587
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@domain2.com [relay2.org]:2525
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@domain3.com
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```
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This will cause email sent from domain3.com to be delivered directly.
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#### References
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Thanks to the author of [this article][1] for the inspiration. This is also worth reading to understand a bit more about how to set up Mailgun to work with this.
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[1]: https://community.rackspace.com/products/f/email-products-forum/3897/how-to-setup-postfix-with-a-mailgun-smtp-relay-when-using-multiple-domains
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