Use SpamScope/mail-parser

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Hello,

There is a lot of different issues related to mail parsing. There is a library whose purpose is to deal with these problems: https://github.com/SpamScope/mail-parser

We will give the critical element to the library (which has no dependencies), which is better tested, so we will have less work and a more stable library.

• We need to evaluate its potential as well as the legitimacy of its use.
• We should maintain backward compatibility.
• We should pass all existing tests.

Greetings,