[FEATURE-Request] Add rbl_override functionality to Postfix

[sknight80]

Description

We want to add a whitelist functionality to postfix to make sure we can get emails from a sender who is trusted but listed on zen.spamhaus.org. More details in #35

Fixes # (issue)

• What is the current behavior (you can also link to an open issue here) ? When we get an email from a sender and the sender is trusted but listed on zen.spamhaus.org postfix will reject the email and will not deliver to rspam.
• What is the new behavior (if this is a feature change) ? Same thing, but before we check the sender in zen.spamhaus.org we check the rbl_override file (postfix map) and if the sender is there and trusted (OK) then we will skip the zen.spamhouse.org verification and pass the email to rspam for validation.

Type of change

Please delete options that are not relevant.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [X] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation only
• [ ] Performance improvement
• [ ] Refactoring (a change that neither fixes a bug nor adds a feature)
• [ ] Test (adding missing tests or correcting existing ones)
• [ ] Other...

Status

• [X] Ready
• [ ] In development
• [ ] Hold

Todo List

• [ ] Implementation
• [X] Tests
• [ ] Documentation
• [ ] ...

How has this been tested ?

I did not tested. I used my solution from one of my oldest hardware/mailserver instances.

Describe the tests that you ran to verify your changes. Provide instructions so we can reproduce and please also list any relevant details of your test configuration.

Actually tested one of my live environment with the following cases:

• [X] Default configuration (I did not attach my custom rbl_override file)
• [X] Attach a custom rbl_orverride file
• [X] Wrong rbl_override file

Test 1 startup log:

mailserver_1    | [INFO] Created default (empty) rbl_override file
mailserver_1    | [INFO] RBL Override initialized

Test 2 startup log:

mailserver_1    | [INFO] /etc/postfix/rbl_override file found
mailserver_1    | [INFO] RBL Override initialized

Test 3 startup log:

mailserver_1    | [INFO] /etc/postfix/rbl_override file found
mailserver_1    | postmap: warning: /etc/postfix/rbl_override, line 2: expected format: key whitespace value
mailserver_1    | [INFO] RBL Override initialized

[sknight80]

CC: @cracker0dks here is the PR. I need to test one of my servers.

[AndrewSav]

LGTM