\s*any whitespace character, repeated any number of times
Non-Capturing Group(?:.*?[:=;]|ORCPT|for|domain of|ESMTPSA id)? ?repeats the group contents below at most once:
.*?any character (except for line terminators), repeated any number of times
:the literal : (5810 / 728 / 3A16)
=the literal = (6110 / 758 / 3D16)
;the literal ; (5910 / 738 / 3B16)
ORCPTthe literal text ORCPT (case insensitive) forthe literal text for (case insensitive) domain ofthe literal text domain of (case insensitive) 5th AlternativeESMTPSA id ESMTPSA idthe literal text ESMTPSA id (case insensitive) \s*any whitespace character, repeated any number of times
Non-Capturing Group(?:"?([\w ]*?)[ "<])? ?repeats the group contents below at most once:
"?optionally matches the literal " (3410 / 428 / 2216)
*?matches any number of characters from the set below:
\wany word character
the literal (3210 / 408 / 2016)
the literal (3210 / 408 / 2016)
"the literal " (3410 / 428 / 2216)
<the literal < (6010 / 748 / 3C16)
\s*any whitespace character, repeated any number of times
<?optionally matches the literal < (6010 / 748 / 3C16)
*?matches any number of characters from the set below:
\wany word character
.the literal . (4610 / 568 / 2E16)
@the literal @ (6410 / 1008 / 4016)
*matches any number of characters from the set below:
\wany word character
.the literal . (4610 / 568 / 2E16)
>?optionally matches the literal > (6210 / 768 / 3E16)
g modifier: global. Finds all matches instead of stopping after the first
i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters