[FR] Support mail system related protocols including smtp, pop3 and imap

[fengnex]

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• I had searched in the issues and found no similar feature requirement.

Description

No response

Use case

let DeepFlow be able to parse standard requests and responses of typical mail systems

Related issues

No response

Are you willing to submit a PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[sharang]

Here is a blog post (currently in Chinese) explaining how to add protocol support to DeepFlow: https://deepflow.io/blog/042-deepflow-extended-parsing-in-practice/ . We look forward to contributions from the community.

[niharikag09]

I'd like to work on this issue. To keep the initial contribution focused and reviewable, I propose starting with SMTP protocol parsing, including request/response detection and unit-test coverage, and handling POP3/IMAP separately afterward. Does this scope and approach align with the maintainers' expectations?