Extracting Email from string in SQL Server

I have a column that contains an email address I am trying to extract.

It normally starts with "User:" and ends right before "TextClient". Tried to use a combination of SUBSTRING and CHARINDEX, returning the values after "User:". Another option was finding "@" and pull everything before and after. I have the following code so far but am pulling too much information.

WITH emailString AS
(
    SELECT 'Text Draft Saved - User: v-test123@blah.com TextClient: Blah' AS st
)
SELECT
    st
    , STUFF(SUBSTRING(st,1,CHARINDEX(' ',st,CHARINDEX('@', st))-1),1, 
    CHARINDEX('@', st) - CHARINDEX(' ',
    REVERSE(SUBSTRING(st,1,CHARINDEX('@', st)-1))),'')  
FROM emailString

I get the following:

SELECT 
    SUBSTRING(
        'Text Draft Saved - User: v-test123@blah.com TextClient: Blah', 
        CHARINDEX('User: ', 'Text Draft Saved - User: v-test123@blah.com TextClient: Blah') + LEN('User: '), 
        CHARINDEX(' TextClient: ', 'Text Draft Saved - User: v-test123@blah.com TextClient: Blah') - (CHARINDEX('User: ', 'Text Draft Saved - User: v-test123@blah.com TextClient: Blah') + LEN('User: '))
    ) AS ExtractedEmail;

or

DECLARE @TestString NVARCHAR(100) = 'Text Draft Saved - User: v-test123@blah.com TextClient: Blah';

SELECT 
    SUBSTRING(
        @TestString, 
        CHARINDEX('User: ', @TestString) + LEN('User: '), 
        CHARINDEX(' TextClient: ', @TestString) - (CHARINDEX('User: ', @TestString) + LEN('User: '))
    ) AS ExtractedEmail;

Fiddler output