Regex Explanation

This should give you a start :)

http://www.regexper.com/#%5E%5B%5Cw!%23%24%25%26'*%2B%5C-%2F%3D%3F%5C%5E_%60%7B%7C%7D~%5D%2B(%5C.%5B%5Cw!%23%24%25%26'*%2B%5C-%2F%3D%3F%5C%5E_%60%7B%7C%7D~%5D%2B)*%40(((%5B%5C-%5Cw%5D%2B%5C.)%2B%5Ba-zA-Z%5D%7B2%2C4%7D)%7C((%5B0-9%5D%7B1%2C3%7D%5C.)%7B3%7D%5B0-9%5D%7B1%2C3%7D))%24

Looks to me email related, although I'm not convinced it's a correct email validation.

From left to right:
- Any word
- A dot followed by a word (any number of times)
- The @ sign

...and then it gets a bit funky... I think the top right part is essentially:

- Any word followed by a dot (any number of times)
- a 2-4 len word

...and the bottom right is an IP address

- 1-3 digits followed by a dot (3 times)
- 1-3 digits

Examples:
longwordwithnospaces@my-website-name.us
bob.jones@blah.com
jim@168.10.1.1

This editor allows you to enter test data and visualise the match.
https://www.debuggex.com

...it doesn't seem to understand the line start and line end in the regex though (the leading ^ and trailing $). Works well with those stripped i.e:

[\w!#$%&'*+\-/=?\^_`{|}~]+(\.[\w!#$%&'*+\-/=?\^_`{|}~]+)*@((([\-\w]+\.)+[a-zA-Z]{2,4})|(([0-9]{1,3}\.){3}[0-9]{1,3}))

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hi.. it is your answer

Expected one of *, +, ?, {, {,, (, [, ., \, $, |, ) at line 1, column 3 (byte 3) after ("

@bigdogman, that's an excellent explanation.

It's worth adding that given that it looks like we're dealing with an email address, the domain of the address can be an ip address (ip4, not ip6) or just a standard domain name, though @ienaxxx already mentioned this.

Wow! I wasn't expecting so many detailed explanations. Thank you all.

@Terry, interesting, I wasn't aware of that. Thanks for the explanation. :-)