Getting "mail transport unavailable" error in Postfix.

Issue

• After configuring /etc/postfix/transport file, getting following error while sending emails:

Jun  2 15:53:11 xxxx postfix/qmgr[20304]: warning: connect to transport private/????smtp: No such file or directory
Jun  2 15:53:11 xxxx postfix/error[20391]: 2500A80251: to=<user@domain.com>, relay=none, delay=0.06, delays=0.04/0.01/0/0.01, dsn=4.3.0, status=deferred (mail transport unavailable)