don't have to add much, but if it's a "standard compliant" mail message:
RFC 2822 seems to state the "Subject:" and other keywords are case-INsensitive, so you should match /From:/i and /Subject:/i, respectively.
Email::Simple, as recommended by Athanasius, does already provide for this and other tiny quirks.

In reply to Re: Matching multiple patterns with regex by soonix
in thread Matching multiple patterns with regex by Tiarcon

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