extract email address from text

Hi,

I want to extract only the email addresses from text string.

this is the text:

       "Bob: Bob@abc, Karen: Karen@cde, Sam: Sam@def"

 expected output: "Bob@abc,Karen@cde,Sam@def"

       "Bob: Bob@abc, Karen: Karen@cde, Sam:Sam@def"

output: "Bob@abc,Karen@cde,Sam@def"

or 

       "Bob: Bob@abc, Karen: Karen@cde,Sam@def"

output: " Bob@abc,Karen@cde,Sam@def"

or 

       "Bob Karen: Karen@cde, Sam: Sam@def"

Output: "Karen@cde,Sam@def"

Thanks,

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