This is not guaranteed to work in all cases (e.g., where @ may appear outside of an email string) but using Jeff Moden's DelimitedSplit8K string splitter, you can try something like this:
DECLARE @t TABLE (EmployeeID INT, Email VARCHAR(200))
INSERT INTO @t
SELECT 1, '<mmooney@gmail.com>;"mmoney@gmail.com"'
UNION ALL SELECT 2, '<chrisgardener@yahoo.com>)'']chrisgardener@comcast.net)]'
UNION ALL SELECT 3, '"natan@hotmail.com'':>"natan@hotmail.com?'''
UNION ALL SELECT 4, '"jennifer@walmart.com}'';jennifer@fedex.com'
SELECT EmployeeID, Email
FROM (
SELECT EmployeeID, Email, ItemNumber
,df=CASE WHEN PATINDEX('%[^0-9A-Za-z@.]%', Item) = 0
THEN Item
ELSE SUBSTRING(Item, 1, PATINDEX('%[^0-9A-Za-z@.]%', Item) - 1) END
FROM @t
CROSS APPLY dbo.DelimitedSplit8K(Email, '@') ds
WHERE CHARINDEX('.', Item) <> 0) x
GROUP BY EmployeeID, Email
HAVING MAX(df) = MIN(df)
The referenced string splitter can be found here: http://www.sqlservercentral.com/articles/Tally+Table/72993/
My thought question: Have you ever been told that your query runs too fast?
My advice:
INDEXing a poor-performing query is like putting sugar on cat food. Yeah, it probably tastes better but are you sure you want to eat it?
The path of least resistance can be a slippery slope. Take care that fixing your fixes of fixes doesn't snowball and end up costing you more than fixing the root cause would have in the first place.
Need to UNPIVOT? Why not CROSS APPLY VALUES instead?[/url]
Since random numbers are too important to be left to chance, let's generate some![/url]
Learn to understand recursive CTEs by example.[/url]
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