How to setup proxy for postfix for sending email?

Question

I can't access Gmail directly, have to use proxy. So when I send email from Emacs "mu4e" client which delivered by postfix. I have setup postfix, but still can't sent out.

Here is the output of command mailq:

-Queue ID-  --Size-- ----Arrival Time---- -Sender/Recipient-------
8BA143C026D    1654 Sun Oct 25 21:25:41  numbchild@gmail.com
         (connect to smtp.gmail.com[64.233.189.108]:587: Connection timed out)
                                         jackkamm@gmail.com
                                         bzg@gnu.org
                                         emacs-orgmode@gnu.org
                                         adrian.kummerlaender@student.kit.edu

140513C026F   21464 Mon Oct 26 10:23:14  numbchild@gmail.com
         (connect to smtp.gmail.com[64.233.189.108]:587: Connection timed out)
                                         jackkamm@gmail.com
                                         emacs-orgmode@gnu.org

-- 22 Kbytes in 2 Requests.

Even I executed command postqueue -f some times. Still not work.

I want to setup proxy for postfix to bypass this firewall block. Does anybody knows how? Any solution or hints are welcome!!