Few days back I did some changes in /etc/postfix/virtual file and restarted the postfix service.Today I saw some error in mail logs stating “hash:/etc/postfix/virtual is unavailable. open database /etc/postfix/virtual.db: No such file or directory”

I checked /etc/postfix/virtual.db about its existence by using command ls -l /etc/postfix/virtual.db and found it was not there.

To resolve this issue one more step to be done which I forgot to run ,it is

postmap /etc/postfix/virtual

Now /etc/postfix/virtual.db file is created and there is no problem seen in mail log also.