[CentOS] setting up postfix

This should be an easy one. I'm trying to get postfix going. I've
never done this before. I followed the directions at
http://wiki.centos.org/HowTos/postfix. I opened port 25:

iptables -I INPUT -p tcp -m tcp --dport 25 -j ACCEPT

Here's an attempt to send mail:

[motor at localhost motor]# mail -v larry.martell at gmail.com
Subject: test
test
.
EOT
larry.martell at gmail.com... Connecting to [127.0.0.1] via relay...
220 localhost.localdomain ESMTP Postfix
>>> EHLO localhost.localdomain
250-localhost.localdomain
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
>>> MAIL From:<motor at localhost.localdomain> SIZE=219
250 2.1.0 Ok
>>> RCPT To:<larry.martell at gmail.com>
>>> DATA
250 2.1.5 Ok
354 End data with <CR><LF>.<CR><LF>
>>> .
250 2.0.0 Ok: queued as D26C8830F
larry.martell at gmail.com... Sent (Ok: queued as D26C8830F)
Closing connection to [127.0.0.1]
>>> QUIT
221 2.0.0 Bye

But I don't receive the mail. In a file in /var/spool/postfix/defer I see:

<larry.martell at gmail.com>: connect to
alt2.gmail-smtp-in.l.google.com[2607:f8b0:400d:c00::1a]:25: Network is
unreachable
recipient=larry.martell at gmail.com
offset=654
dsn_orig_rcpt=rfc822;larry.martell at gmail.com
status=4.4.1
action=delayed
reason=connect to
alt2.gmail-smtp-in.l.google.com[2607:f8b0:400d:c00::1a]:25: Network is
unreachable

Have I missed a step or done something wrong?

TIA!
-larry