hi vidyaR
Make sure that the reply to address is correct, and ask users to put the word unsubscribe in the subject.
Setup a scheduled task to run checkmail.cfm every 5 or 10 minutes. Checkmail.cfm should get all mail from the account in question, say listserv@yoursite.com. It should then loop through all of the messages returned, and check if the word unsubscribe exists in the subject. If it does, run a query to delete from or deactivate the record of your email list table where the email address matches that of the current message. The final command in the loop should be to delete the message from the server, if you want to clean it up.
Try this:
<CFPOP
server="mail.yoursite.com"
username="listserv"
password="xx"
action="getheaderonly"
name="getmail">
<CFLOOP query="getmail">
<CFSET temp.msgnum = messagenumber>
<CFSET temp.subject = trim(subject)>
<CFSET temp.email = from>
<CFIF ucase(temp.subject) contains ucase("unsubscribe"

>
<CFQUERY name="updEmailList" datasource="ds1">
update emaillist
set active = false
where upper(email) = '#ucase(from)#'
</CFQUERY>
</CFIF>
<!--- delete if you want
<CFPOP
server="mail.yoursite.com"
username="listserv"
password="xx"
action="delete"
messagenumber="#temp.msgnum#">
--->
</CFLOOP>