Why Salesforce does not accept my REGEX?

Question

I have a RegEx created and tested in regex platforms, this one:

;.+$

If I check its functionality the result is okay, you could check it too in this link https://regex101.com/r/ocDofm/1/.

The problem is that, when I implement it into a Validation Rule for a Specific field, it does not work. My Validation Rule is :

REGEX( Email__c, ';.+$')

And, if I put the same text that I use on regex101.com web, the Validation Rule does not run. For example, if I open Email__c field, which is a Long Text Area field, and I put this text;

test@test.com;test2@test.com;and so on...

Validation Rule should work and error message should appear, but it happens nothing.

Any idea? Thanks.

EDIT: There is an example of the text that I want to be possible in the Email__c field:

john@gmail.com;
anne@gmail.com;
lewis@gmail.com;

So, the next text, should fire the Validation Rule:

john@gmail.com;a
anne@gmail.com;
lewis@gmail.com;

Answer 1

That's because SFDC matches the whole field against your REGEX, your whole Email__c is not only ';.+$', plus $ is a special character, so you need something like this

REGEX( Email__c, '.*[;.+$].*')

If you're only interested in ; character then put it like this '.*;.*'

Another point is that if you are only curious about ; character you can use CONTAINS(Email__c, ';')

UPDATE:

Try this one .*;[^\n].*, this should only trigger when you don't have new line after ;

UPDATE2:

REGEX( Email__c, '((.||(\r?\n))*;.((\r?\n)||$)(.||(\r?\n))*)')