Hi，
After you clicked reply， did you send the mail? If you sent the mail and
still see the draft mail got saved, could you please retest the behavior by adding
user parameter WCF_IGNORE_ENHANCEMT with value set as A in T-code: su3?
If the issue still shows up，you can do the debugging around the method in note
below.
1306333 - Email should not automatically save without clicking on save
1614899 - Draft not updated to Sent in IR after sending draft email
Best Regards,
Bruce