[WIP] Fix the 'Reply' button behavior, align it with Gmail

[limonte]

This PR aligns the behavior of the 'Reply' button with Gmail:

• if from !== acctEmail => reply to the from email address only
• if from === acctEmail then reply to all to email addresses (excluding cc and bcc)

close #4077

TODO: tests

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Tests (delete all except exactly one):

• Tests added or updated

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To be filled by reviewers

I have reviewed that this PR... (tick whichever items you personally focused on during this review):

• addresses the issue it closes (if any)
• code is readable and understandable
• is accompanied with tests, or tests are not needed
• is free of vulnerabilities
• is documented clearly and usefully, or doesn't need documentation

[limonte]

Closing in favor of #4107