feat: Add list of allowed recipient domains

[dosmanak]

discard all email for not listed domains

Description of the change

Regarding an issue #90 but not exactly. This Feature enables to setup nonprod smtp-relay that allows to send e-mails only to allowed domains.
Other e-mails are silently discarded.

Motivation and Context

Tested application allows to send any e-mail without error but only particular recipient domains get through.

How Has This Been Tested?

podman run --rm -p 2525:25 -e SMTP_SERVER=smtp.sendgrid.net -e SMTP_USERNAME=apikey -e SMTP_PASSWORD=xxxxx -e SERVER_HOSTNAME=company.tld -e ALLOW_DOMAINS=gmail.com docker-postfix:transport_map

swaks --to studenyp@gmail.com --from test@company.tld --server localhost:2525

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (adding or updating documentation)

Checklist:

• My change requires a change to the documentation and I have updated the documentation accordingly.
• My change adds a new configuration variable and I have updated the .env.example file accordingly.

And lastly, many thanks for taking your time to help us improve this project !

[juanluisbaptiste]

Hi @dosmanak, thanks for your PR.

Code LGTM, will test it and let you know.

[juanluisbaptiste]

After various container restarts, the allowed domains are being duplicated in the /etc/postfix/transport file:

e4a07a47e63f:/# grep gmail /etc/postfix/transport 
gmail.com :
gmail.com :
gmail.com :

And the container logs:

postfix-1  | Nov 10 22:06:23 correo postfix/master[1]: daemon started -- version 3.10.5, configuration /etc/postfix
postfix-1  | Nov 10 22:06:46 correo postfix/smtpd[96]: connect from unknown[172.23.0.1]
postfix-1  | Nov 10 22:06:46 correo postfix/trivial-rewrite[98]: error: /etc/postfix/transport, line 320: duplicate entry: "gmail.com"
postfix-1  | Nov 10 22:06:46 correo postfix/trivial-rewrite[98]: warning: texthash:/etc/postfix/transport is unavailable. /etc/postfix/transport, line 320: duplicate entry: "gmail.com"
postfix-1  | Nov 10 22:06:46 correo postfix/trivial-rewrite[98]: warning: texthash:/etc/postfix/transport lookup error for "*"
postfix-1  | Nov 10 22:06:46 correo postfix/trivial-rewrite[98]: warning: texthash:/etc/postfix/transport is unavailable. /etc/postfix/transport, line 320: duplicate entry: "gmail.com"
postfix-1  | Nov 10 22:06:46 correo postfix/trivial-rewrite[98]: warning: texthash:/etc/postfix/transport lookup error for "*"
postfix-1  | Nov 10 22:06:46 correo postfix/trivial-rewrite[98]: warning: texthash:/etc/postfix/transport is unavailable. /etc/postfix/transport, line 320: duplicate entry: "gmail.com"
postfix-1  | Nov 10 22:06:46 correo postfix/trivial-rewrite[98]: warning: texthash:/etc/postfix/transport lookup error for "juan@juanbaptiste.tech"
postfix-1  | Nov 10 22:06:46 correo postfix/trivial-rewrite[98]: warning: transport_maps lookup failure
postfix-1  | Nov 10 22:06:46 correo postfix/trivial-rewrite[98]: warning: texthash:/etc/postfix/transport is unavailable. /etc/postfix/transport, line 320: duplicate entry: "gmail.com"
postfix-1  | Nov 10 22:06:46 correo postfix/trivial-rewrite[98]: warning: texthash:/etc/postfix/transport lookup error for "user@xxxxx.tld"
postfix-1  | Nov 10 22:06:46 correo postfix/trivial-rewrite[98]: warning: transport_maps lookup failure
postfix-1  | Nov 10 22:06:46 correo postfix/smtpd[96]: NOQUEUE: reject: RCPT from unknown[172.23.0.1]: 451 4.3.0 <user@xxxxx.tld>: Temporary lookup failure; from=<juan@xxxxx2.tld> to=<user@xxxxx.tld> proto=ESMTP helo=<mylaptop>
postfix-1  | Nov 10 22:06:46 correo postfix/smtpd[96]: disconnect from unknown[172.23.0.1] ehlo=1 mail=1 rcpt=0/1 quit=1 commands=3/4

[dosmanak]

I have not assumed the scenario where the container restarts as I always delete it. Will look into it.

[juanluisbaptiste]

When the container is restarted, for example because the docker daemon was restarted because of an upgrade, or a server restart, in such cases the containers will not be recreated and this will happen.

[dosmanak]

I added simple truncate of the file prior addind allowed domain and discard default. The solution is not very extendable but for now I think it will serve its purpose.

[juanluisbaptiste]

I think it would be cleaner if you look for the string you are adding first, instead of blindly adding it and truncate it before doing that. What if another feature in the future also touches that file?

[juanluisbaptiste]

@dosmanak did you have some time to update this PR?

[dosmanak]

I think it would be cleaner if you look for the string you are adding first, instead of blindly adding it and truncate it before doing that. What if another feature in the future also touches that file?

Well I did not planned it to be super strong. But I will look into that.

[dosmanak]

What about this? Still not great, as it does not concerns line orders...