Not having access to a designer right now but the logic would be as follow

1. Loop through all value on that field

2. If it contain "@" then add into another variable

Assuming that field name is Internet Field then the code would be similar to :

NewField := "";

@For(i:= 0; i < @Elements(InternetField); i := i + 1; @Do(

@If(@Contains(InternetField[i]; "@"); NewField := NewField : InternetField[i]; "")

));

@Trim(NewField);

Beware that the above formula might throw an error due to typos and incorrect syntax.