feat(heuristics): add Fake Email analyzer to validate maintainer email domain

[AmineRaouane]

Summary

This PR adds a new heuristic analyzer called FakeEmailAnalyzer. It verifies the validity of maintainer email addresses listed in a PyPI package by checking both the format and the existence of MX records for their domains. This helps detect packages with fake or throwaway emails, which are often indicative of malicious intent.

Description of changes

• Implemented FakeEmailAnalyzer that:
  • Validates email format using a regex.
  • Verifies the existence of MX records for the email domain via DNS resolution.
• Updated detect_malicious_metadata_check.py to include and invoke this new analyzer.
• The analyzer handles DNS errors and skips analysis if no email is present.
• The logical reason for combining quickUndetailed with a failed(Heuristics.FAKE_EMAIL.value) is that a package that is rushed onto a platform by someone using a fake email address points to an actor who may be trying to quickly distribute a package while obscuring their identity and avoiding being investigated.

Related issues

None

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[benmss]

Suggested change

	- **Description**: Checks if the package maintainer or author has a suspicious or invalid email .
	- **Description**: Checks if the package maintainer or author has a suspicious or invalid email.

[benmss]

Suggested change

	- **Rule**: Return `HeuristicResult.FAIL` if the email format is invalid or the email domain has no MX records ; otherwise, return `HeuristicResult.PASS`.
	- **Rule**: Return `HeuristicResult.FAIL` if the email format is invalid or the email domain has no MX records; otherwise, return `HeuristicResult.PASS`.

[benmss]

Validating email addresses is a complex task. What we have here is more like a sanity check, verifying that the address is vaguely of the right format. That may be enough for the purpose of this check, in which case this method should be renamed and re-documented to make that clear. Alternatively, if we do really want to ensure that email addresses are valid, this method will need to be expanded considerably. @behnazh-w
See the top two answers on this stackoverflow thread for more information: https://stackoverflow.com/questions/2049502/what-characters-are-allowed-in-an-email-address

[benmss]

As part of the above, I think the regex checking and dns resolution steps should be split into separate functions. This could also simplify the related tests.

[benmss]

Another alternative is to use the Python library email-validator to more formally validate emails. It also uses dnspython, but handles some of the more complicated validation aspects.
https://pypi.org/project/email-validator/

[AmineRaouane]

i used the email-validator approach