Hi Tahir,
Schedule Dunning Program (RF150SMS) along with printing with LP01 as a default printer.Then schedule a program for sending mail.That Z program should be made as such that it converts the spool made after dunning run (with the help of FM CONVERT_OTF_2_PDF ) into PDF and it should fetch the mail ID from the Customer master and them mail the specific pdf letter to that user.
The program for Customer email address is already given by You just need the help of ABAP for the development of the program.
By scheduling both these programs with a time gap of say 1 hour, your requirement can be met.
Hope Icould be some help to you!
Regards,
Siddharth Khandelwal