getting error
fatal: /etc/postfix/master.cf: line 12: bad transport type: content_filter=dfilt:

my master.cf is
smtp inet n - n - - smtpd
-o content_filter=dfilt:
dfilt unix – n n – – pipe
flags=Rq user=filter argv=/etc/postfix/disclaimer -f ${sender} — ${recipient}

You need to read the "Question Guidelines" link in my posting signature. Without details, no one will be able to help you. You don't tell us what version/distro of Linux you're using, version of postfix, whether this is a new problem/installation, etc. Also, the error is clearly saying that there is an error on line 12 in your master.cf file...but what you've posted doesn't have 12 lines.

Regardless, there are two things to check. First, is there a space at the beginning of the dfilt line??. Postfix treats space as line continuation so that would cause a problem. Second thing: did you actually create that user filter you're referencing? Have you read through the Postfix documentation?