An alternative would be to union the email addresses e.g.
DECLARE @Result int
declare @tbl1 table (id1 int identity(1,1), email1 varchar(30))
declare @tbl2 table (id2 int identity(1,1), email2 varchar(30))
insert into @tbl1 values('email1'),('email2'),('email3')
insert into @tbl2 values('email4'),('email2'),('email5')
if exists (select top 1 * from (select email1 from @tbl1 union select email2 from @tbl2) t where email1=@email)
set @Result= 1
else
set @Result= 0
return @Result