docs: fix #47146 – improve email validation regex to prevent invalid formats

[Gurry-12]

What this PR does:

This PR updates the email validation regex in the How to verify that strings are in valid email format article to address an issue where invalid characters (like commas) were being accepted.
Problem:

The current regex pattern:

^[^@\s]+@[^@\s]+.[^@\s]+$

allows email addresses like surname123@gmail.,com, which are structurally invalid.
Fix:

Replaced the regex pattern and its explanation with a more accurate expression:

^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+.[a-zA-Z]{2,}$

This change:

Restricts characters in the local and domain parts to common valid characters.

Ensures the TLD has at least two alphabetical characters.

Still remains readable and practical for general validation.

Related issue:

Fixes #47146

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Internal previews

📄 File	🔗 Preview link
docs/standard/base-types/how-to-verify-that-strings-are-in-valid-email-format.md	How to verify that strings are in valid email format

[Gurry-12]

@dotnet-policy-service agree

[adegeo]

Hello, thank you for this pull request, but we're not looking to improve this page with more complex examples. The article states this, which is a policy we're following:

If you try to create the perfect regular expression to validate that the structure of an email is correct, the expression becomes so complex that it's incredibly difficult to debug or improve. Regular expressions can't validate an email exists, even if it's structured correctly. The best way to validate an email is to send a test email to the address.

[Gurry-12]

thank you for your revert @adegeo sir, It will really help me to improve my understanding towards the contributions.