Regular Expressions 101

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/
^(?:\")?(?:\w+(?:\.|\_|\<)?)+\w+(?:\")?@(?:\w+\.)+\w{2,}(?:\>)?$
/
gm
^ asserts position at start of a line
Non-capturing group
(?:\")?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\" matches the character " with index 3410 (2216 or 428) literally (case sensitive)
Non-capturing group
(?:\w+(?:\.|\_|\<)?)+
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\w
matches any word character (equivalent to [a-zA-Z0-9_])
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
Non-capturing group
(?:\.|\_|\<)?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
1st Alternative
\.
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
2nd Alternative
\_
\_ matches the character _ with index 9510 (5F16 or 1378) literally (case sensitive)
3rd Alternative
\<
\< matches the character < with index 6010 (3C16 or 748) literally (case sensitive)
\w
matches any word character (equivalent to [a-zA-Z0-9_])
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
Non-capturing group
(?:\")?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\" matches the character " with index 3410 (2216 or 428) literally (case sensitive)
@ matches the character @ with index 6410 (4016 or 1008) literally (case sensitive)
Non-capturing group
(?:\w+\.)+
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\w
matches any word character (equivalent to [a-zA-Z0-9_])
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
\w
matches any word character (equivalent to [a-zA-Z0-9_])
{2,} matches the previous token between 2 and unlimited times, as many times as possible, giving back as needed (greedy)
Non-capturing group
(?:\>)?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\> matches the character > with index 6210 (3E16 or 768) literally (case sensitive)
$ asserts position at the end of a line
Global pattern flags
g modifier: global. All matches (don't return after first match)
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
Your regular expression does not match the subject string.

Regular Expression
No Match

/
/
gm

Test String