Lotus Domino 8.5 / User Mail File not deleted after user removed

I have Lotus Domino 8.5.3 FP6 on Windows 2008 (64bi).

Few time back , I added cluster server for Domino. its working fine, both servers can replicate mails with each other correctly & when creating new user, it creates mail file on both servers fine. Archiving is also enabled which moves 1 year old mails into user archive file.

The problem is whenever I DELETE any user from the DOMINO server, it does not REMOVE user mail nsf file from both servers. Also it does not remove this user from the users groups, So it's quite a headache for me to first delete user from USERS, then Delete user mail files (that includes current mail nsf + archive file )from both servers , then remove users from each user groups. (all done from domino admin client)

What should I check ?