I could get the disclaimer enabled based on the domain.Followed following steps.

[FAQ] How to enable signing disclaimer on outgoing mails? (Page 1) - iRedMail General Technical Support - iRedMail - Free, Open Source Mail Server Software for Linux/BSD

The appropriate discliamer files to be maintained in /opt/zimbra/data/altermime/domain1.txt
/opt/zimbra/data/altermime/domain1.html