I have configured Sendmail as Mail Transport Agent and procmail as Local Delivery agent.I have also enabled quota system on filesystem on partition /var.
Each user can have 10MB quota as soft limit and 11MB quota as Hard limit.Over exceding either hard limli or expiration of grace period (which actually start when soft limit is exceeded),sender will not be able to send mail and procmail bounch the sender's mail to himself informing that receipent's quota is exceeded....upto here no problem........but my prob is .........how receipent knows that his quota is full so that he is not getting mail from sender?.......Is there any way that procmail send quota full msg when receipent cross soft limit......Please help me ..........i have to implentment it on online mailserver as soon as possible .

See warnquota function.

Thanks velda.ebel............u at least gave me a hope..........But i don't understand warnquota function............is it in built function of procmail or what?...........please guide na...

No
warnquota is a inherent linux command
do a #man warnquota to see how to use it.
it is not a background process, so you might want to cron it, and run it (for example) once a week.