Hi Amol Khochare,
you may do yourself and us a favor and split your program into functional modules: FORM/FUNCTION/METHODs for the various tasks, i.e. getting the attachment data, convert whatever it is to binay format, add mail address as recipient and so on.
Avoid the use of global variables like gt_useremail because you don't need them.
Run program check with ATC ABAP test cockpit and change program until you don't get any errors/warnings.
Let us know what te code looks like then!
Regards Clemens