Contrary to what the title implies the content mentions it's not actually RFC 822 compliant and while it is certainly an impressive regex to behold RFC 822 was already long obsoleted when this was published.
My project https://github.com/dhoerl/EmailAddressFinder constructs a rfc5322 compliant regex by building up small verifiable pieces. You can option comments up to an arbitrary depth. There is a test suite from another interested party that this regex succeeds 100%.
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[ 2.9 ms ] story [ 19.9 ms ] threadhttps://metacpan.org/release/Email-Valid/source/lib/Email/Va...