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Regex: How to valid domain part not in email have all numeric

I am struggling with one issue where I need to verify domain part should not all be numeric.
For example:
abc#123.com -> Invalid
abc#1abc.com -> valid
Regex:
^(?=(.{1,64}#.{1,255}))((?!.*?[._]{2})[!#$%&'*+\-\/=?\^_`{|}~a-zA-Z0-9}]{1,64}(\.[!#$%&'*+\-\/=?\^_`{|}~a-zA-Z0-9]{0,}(?<!\.)){0,})#((\[(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)(\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}\])|((?!-)(?=.*[a-zA-Z])[a-zA-Z0-9-]{1,63}(?<!-)(\.(?!-)[a-zA-Z0-9-]{1,63}(?<!-)){1,}))$
Above regex need modification because there are some other validation which is working fine with above regex. Only thing is pending to validate domain part should not all numeric.
Updated:
After some research on above regex
I am able to segregate emails in to different groups. Now for group 10 need to add validation if all characters in group 10 string are aplha numeric.
Regex:
^(?=(.{1,64}#.{1,255}))((?!.*?[._]{2})[!#$%&'*+\-\/=?\^_`{|}~a-zA-Z0-9}]{1,64}(\.[!#$%&'*+\-\/=?\^_`{|}~a-zA-Z0-9]{0,}(?<!\.)){0,})#((\[(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)(\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}\])|((?!-)(?=.*[a-zA-Z])((?:.*[a-zA-Z0-9]))[a-zA-Z0-9-]{0,63}(?<!-)(\.(?!-)[a-zA-Z0-9-]{1,63}(?<!-)){1,}))$
Explore regex on : https://regex101.com/
TIA

There's no point in doing this - the fact that an email fulfills the requirements as set forth in RFC5322 does not mean it's a valid email address: The only way to know that, is to send an email to it, and have the user reply to it, follow a link inside it, or copy a code/token inside it.
Given that you have to do that anyway, that will also pick up any issues with invalid email addresses. Thus, the correct validation for email is:
Pattern.compile("^.+#.+\\..+$")
(Assuming you don't want single
and this does what you want, which is, filter out obvious incorrect entries, and that's all you need.
If you insist in continuing your mistake, there's always emailregex.com, which has the regex and explains how it works.
NB: Note that you're just wrong. 12345#678.cde can easily be valid - com may not allow you to register a domain that consists solely of digits, but it's not an inherent limitation of the DNS system: Domain parts can be all numbers. The top level domain cannot be, at least, for now, but any other part of it can be. Thus, rejecting foo#123.com is only possible if you program in, on a per-TLD basis, the exact rules. Which also means you need to sign up to the mailing list of every TLD operator to check for any changes they make. You'll be updating that regex every other week. Told you it's a silly thing to want to do!

u can use this to detect the invalid ones.
^\w+([-+.']\w+)*+#\d+.com
just change the .com to which postfix you like.

Custom - Javascript regular expression to validate custom email addresses

I want it to be correct my JavaScript regex pattern to validate below email address scenarios
msekhar#yahoo.com
msekhar#cs.aau.edu
ms.sekhar#yahoo.com
ms_sekhar#yahoo.com
msekhar#cs2.aau.edu
msekhar#autobots.ai
msekhar#interior.homeland1.myanmar.mm
msekhar1922#yahoo.com
msekhar#21#autobots.com
\u001\u002#autobots.com
I have tried the following regex pattern but it's not validating all the above scenarios
/^[_a-z0-9]+(\.[_a-z0-9]+)*#[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,4})$/
Could any one please help me with this where am doing wrong?

The following regex should do:
^(([^<>()\[\]\.,;:\s#\"]+(\.[^<>()\[\]\.,;:\s#\"]+)*)|(\".+\"))#(([^<>()[\]\.,;:\s#\"]+\.)+[^<>()[\]\.,;:\s#\"]{2,})$
Test it: https://regex101.com/r/7gH0BR/2
EDIT: I have added all your test cases

I have always used this one but note it doesn't trigger on escaped unicode:
^([\w\d._\-#])+#([\w\d._\-#]+[.][\w\d._\-#]+)+$
You can see how it works here: https://regex101.com/r/caa7b2/4

First off [_a-z0-9]+ is going to match the username fields for the majority of those testcases. Anything further testing of username field content will result in a mismatch. If you write a pattern that expects two .-delimitered fields, it'll match when you provide two .-delimitered fields and only then, not anything else. Make a mental note of that. I think you probably meant to put the . in the first character set, and omit this part here: (.[_a-z0-9]+)...
As for the domain part of the email address, similar story there... if you're trying to match domains containing two labels (yahoo and com) against a pattern that expects three... it's going to fail because there's one less label, right? There are domain names that only contain one label which you might want to recognise as email addresses, too, like localhost...
You know, there is a point to where you can dig yourself down a very deep rabbit hole trying to parse email addresses, much to the effect of this question and answer sequence. If you're making this complex using regular expressions... I think maybe a better tool is a proper parser generator... otherwise, write the following:
A pattern that matches anything up until an # character
A pattern that matches the # character (this will help you learn how to avoid your .-related error)
A pattern that matches everything (this will help you understand your .-related error)
Combine the three above in the order presented.

regex - repeated or distributed characters

newbie here on regular expressions hoping to get some help.
I have a task to build a regex based on allowed number of repeated or distributed characters.
Here is the regex that I have built but it is not working, only matches on repeated characters.
/(.).*\1{2}/g
if my string is "test", the regex should find a match. If the quantifier is 3 and my string is "1234343" the regex should find a match.
This task is part of a bigger project where the user can configure settings for both username and password on html page, and on form submit it will call java servlet to construct the regex and save it into the database.
Whenever user navigates to reset password page it will send back the regex to javascript to validate the new password, the validation will also be done on the server-side.
I am trying to build a javascript friendly regex that would also work in java.
Any tips are greatly appreciated. I know lookbehind in javascript is not supported, but I don't know what else to keep in mind when constructing the regex.

I think you are looking for:
(.)(.*\1){2}
This will find a character which is repeated 3 times.
(.)_________ captures first occurrence of a character.
___(.*\1)___ finds the character again, after 0 or more other characters ...
_________{2} repeating twice, for a total of 3 occurrences.
You needed (___)’s around the part you wanted {__} repeats. And you want 1 less than the number of occurrences in the {__}, because the (.) already counts for 1 occurrence.

Combining RegEx's

I have two regex's that I am trying to combine. One is email specific and the other checks certain special characters. I have arrived at this solution following much toying:
"^([-0-9a-zA-Z.+_]+#[-0-9a-zA-Z.+_]+\.[a-zA-Z]{2,4}|[\\w\\-ÀÈÌÒÙàèìòùÁÉÍÓÚÝáéíóúýÂÊÎÔÛâêîôûÃÑÕãñõÄËÏÖÜŸäëïöüŸçÇŒœßØøÅåÆæÞþÐð _]){0,80}$"
It does seem to check what I need it to, but for instance the following is still returned valid: abc#foo it does not force a full email address.
Am I using the correct approach or is there a simpler way to structure this RegEx? I'm on a learning curve with regex so all advice appreciated.

Move the multiplier {0,80} inside the parenthesis:
"^([-0-9a-zA-Z.+_]+#[-0-9a-zA-Z.+_]+\.[a-zA-Z]{2,4}|[\\w\\-ÀÈÌÒÙàèìòùÁÉÍÓÚÝáéíóúýÂÊÎÔÛâêîôûÃÑÕãñõÄËÏÖÜŸäëïöüŸçÇŒœßØøÅåÆæÞþÐð _]{0,80})$"
// here __^^^^^^^
Also [a-zA-Z]{2,4} is really poor to validate TLDs, have a look at IANA.
And me#localhost is a valid email address.

How can I remove escaping from a RegExp pattern?

I'm trying to simplify input for a particular regex for my users. A simple example of the regex might be
\b(C|C\+\+|Java)\b
I'm now giving the user the option of appending another branch at the end of the regex by inputting the raw string into a <input type="text"> field. The branch will be interpreted literally, so I need to escape it. I've used https://stackoverflow.com/a/2593661/785663 to get RegExp.quote to do this. I then store the complete regex in a database.
Now, when I retrieve the regex from the database and split it back up and display the branches to the user, I need to remove all the escape characters again. Is there some pre-made function for this or do I need to roll my own?
Yes, I know I ought to replace this with a list of strings to search for. But this only a part of a larger (regex based) picture.

The optimal solution is to change your design: store the unescaped regex, then only escape it when you actually use it. That way you don't have to worry about this messy business of converting it back and forth all the time.
If you use this regex a lot and are worried about the overhead of having to escape it all the time, then store both the unescaped and escaped versions. Update both whenever the user makes a change.
p.s. Allowing user-entered regexes may make your site vulnerable to attack. (Update: Though in this case it is less likely to be a problem, since you are only allowing literal strings)