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When an alias has a remote destination, chasquid uses sender rewriting (also known as SRS [1]) to forward the email without risking being in violation of SPF policies. See https://en.wikipedia.org/wiki/Sender_Rewriting_Scheme for more details. This, however, wasn't documented anywhere, as noted in https://github.com/albertito/chasquid/issues/6. This patch adds a paragraph to the alias documentation explaining this behaviour.
99 lines
3.0 KiB
Markdown
99 lines
3.0 KiB
Markdown
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# Aliases
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[chasquid] supports [email aliases], which is a mechanism to redirect mail
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from one account to others.
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## File format
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The aliases are configured per-domain, on a text file named `aliases` within
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the domain directory. So like `/etc/chasquid/domains/example.com/aliases`.
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The format is very similar to the one used by classic MTAs (sendmail, exim,
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postfix), but not identical.
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### Comments
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Lines beginning with `#` are considered comments, and are ignored.
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### Email aliases
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To create email aliases, where mail to a user are redirected to other
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addresses, write lines of the form `user: address, address, ...`.
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The user should not have the domain specified, as it is implicit by the
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location of the file. The domain in target addresses is optional, and defaults
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to the user domain if not present.
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For example:
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```
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# Redirect mail to pepe@ to jose@ on the same domain.
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pepe: jose
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# Redirect mail to flowers@ to the indvidual flowers.
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flowers: rose@backgarden, lilly@pond
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```
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Destination addresses can be for a remote domain as well. In that case, the
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email will be forwarded using
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[sender rewriting](https://en.wikipedia.org/wiki/Sender_Rewriting_Scheme).
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While the content of the message will not be changed, the envelope sender will
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be the constructed from the alias user.
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User names cannot contain spaces, ":" or commas, for parsing reasons. This is
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a tradeoff between flexibility and keeping the file format easy to edit for
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people. User names will be normalized internally to lower-case. UTF-8 is
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allowed and fully supported.
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### Pipe aliases
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A pipe alias is of the form `user: | command`, and causes mail to be sent as
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standard input to the given command.
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The command can have space-separated arguments (no quotes or escaping
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expansion will be performed).
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For example:
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```
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# Mail to user@ will be piped to this command for delivery.
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user: | /usr/bin/email-handler --work
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# Mail to null@ will be piped to "cat", effectively discarding the email.
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null: | cat
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```
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## Processing
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Aliases files are read upon start-up and refreshed every 30 seconds, so
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changes to them don't require a daemon restart.
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The resolver will perform lookups recursively, until it finds all the final
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recipients. There are recursion limits to avoid alias loops. If the limit (10
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levels) is reached, the entire resolution will fail.
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Commands are given 30s to run, after which it will be killed and the execution
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will fail. If the command exits with an error (non-0 exit code), the delivery
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will be considered failed.
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The `chasquid-util` command-line tool can be used to check and resolve
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aliases.
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## Hooks
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There are two hooks that allow more sophisticated aliases resolution:
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`alias-exists` and `alias-resolve`.
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If they exist, they are invoked as part of the resolution process and the
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results are merged with the file-based resolution results.
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See the [hooks](hooks.md) documentation for more details.
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[chasquid]: https://blitiri.com.ar/p/chasquid
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[email aliases]: https://en.wikipedia.org/wiki/Email_alias
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