Code:
SELECT STRIP(SMTPUID) CONCAT '@' CONCAT STRIP(DOMROUTE)
  INTO :Mail                                           
  FROM QUSRSYS.QATMSMTPA A, QUSRSYS.QAOKL02A B         
 WHERE B.WOS1USRP = USER AND A.USERID = B.WOS1DDEN     
   AND A.ADDRESS = B.WOS1DDGN;