Need to generate automatic approval mail while releasing invoice.

Hi,

we are having a Z report to release invoice as per authorisation matrix. The Selection screen of the report is attached below.

Selection Screen:

output Screen:

in output screen whenever user is trying to release invoice by selecting check box approval mail need to generate to depending amount has been selected in SS. Approval levels are (L1, L2 and L2). After generating the mail if Level1 approves then only invoice needs to release  or else it needs to reject

This is the requirement. I have searched for it but didn't get solution . .Please help me on this.

Thanks in Advance...!