Forward to external email best practices

[bouthors]

#118 cover the same question but with less details.

I would like to have some "virtual" mailbox redirected to external email (like a gmail account).
Example is: virtual@mydomain.com redirected to destination@gmail.com

I did succeed with "rewrite" of rcpt or Sieve at data stage with the following results:

• rewrite at rcpt is replacing the destination email and stalwart smtp service which means:
  • it's considered as a relay if the source external, relay must be allowed as well
  • gmail will fail on spf because stalwart server is not registered in spf record for the original "from" domain
• on the other hand, Sieve script with redirect seems better:
  • mailbox must be created for the email to be accepted
  • no relay, gmail is displaying "via mydomain.com" and spf is validating postmaster@mydomain.com instead of the initial "from". But there is an antispam sieve script by default and I am not expert.

Can you confirm Sieve is the best way to achieve the redirect?
Is the following configuration a good one?

[sieve.trusted.scripts]
spam-filter-with-redirects = '''
require ["envelope", "include"];
include :global "spam-filter";
if envelope :is "to" "virtual@mydomain.com"
{
  redirect "destination@gmail.com";
}'''
track-replies-with-redirects = '''
require ["envelope", "include"];
include :global "track-replies";
if envelope :is "to" "virtual@mydomain.com"
{
  redirect "destination@gmail.com";
}'''
[session.data]
#script = [ { if = "authenticated-as", eq = "", then = "spam-filter"},
#           { else = "track-replies" } ]
script = [ { if = "authenticated-as", eq = "", then = "spam-filter-with-redirects"},
           { else = "track-replies-with-redirects" } ]

[mdecimus]

Yes, at the moment a Sieve script is the best way to redirect messages to external domains.

[bouthors]

Thanks @mdecimus for this feedback. Do you think my sieve example is the good way (leave antispam rules and redirect after) or it's better to redirect before and disable antispam (and let destination MTA do the antispam).
I ask because I am new to sieve and I am not able to know if antispam rules could affect redirect itself.
Please let me know if you have any recommendation.

[mdecimus]

The script looks correct, you may want to add a stop statement if you are not interested in running the spam filter after a message is redirected.

[h3ndrik]

Is there a way to run multiple sieve scripts on data stage? So I can leave the 'spam-filter' and 'track-replies' in place and run my custom script after that? What would be the syntax?

[mdecimus]

You can't run multiple scripts from an expression but what you can do is to have one main script that includes multiple subscripts. Add your scripts to Stalwart as you would normally do and reference them using the include Sieve command.

[maggu]

This is in essence my entire use case I had hoped Stalwart would solve.

I want to accept email for various domains, and forward them to external addresses without SPF causing a reject. In other words, SRS is an absolute must in the modern (in my humble opinion rather broken) world, and neither Sendmail nor Postfix (or, more precisely, the milters that exist) are great at handling it. Also ARC, correct DKIM handling and other things that are a pain to configure properly.

In other words, it would be fantastic if this was a simple thing to accomplish in Stalwart. That is, to be able to just set up an address and specify a forwarding endpoint. (Well, as easy as these things get, but at least without having to know the standards in detail.)

I have half a mind to write an enhancement request for it, but I wanted get some opinions first. Could forwarding address perhaps just be another field under user account settings?