Description of problem:
postfix.spec (2.5.1-1) puts in:

321 inet_protocols = all        (enable IPv4, and IPv6 if supported)

to main.cf during %install. See postconf(5):

Empty lines and whitespace-only lines are ignored, as are lines whose first
non-whitespace character is a #

So, per syntax, comments must be standalone and must have #. This fails on both
counts; it's invalid syntax. Suggest replacing with:

# (enable IPv4, and IPv6 if supported)
inet_protocols = all

across two lines.

Version-Release number of selected component (if applicable):
postfix-2.5.1-1

How reproducible:
rpm -i
http://koji.fedoraproject.org/packages/postfix/2.5.1/1.fc9/x86_64/postfix-2.5.1-1.fc9.x86_64.rpm

Steps to Reproduce:
1. install rpm-based distro
2. run rpm -i
http://koji.fedoraproject.org/packages/postfix/2.5.1/1.fc9/x86_64/postfix-2.5.1-1.fc9.x86_64.rpm
3. profit? no, you can't profit, mail isn't working.
  
Actual results:
in %post, 
postfix: fatal: unknown inet_protocols value "(enable" in "all        (enable
IPv4, and IPv6 if supported)"

Expected results:
some other issue that's causing 2.5.1-1 to not start clean on a virgin install
that I need to look into next

Additional info:
also affects 2.4.6 builds, not present postfix-2.3.3-2