how to change port mail server. my ISP blocked Port 25/26

this is error message connection time out if i send email to gmail account or other.

(connect to alt4.gmail-smtp-in.l.google.com[74.125.21.27]:25: Connection timed out)

I'm asking ISP and they answer, blocked port 25/26 can we change port mail server in centos web panel?

I'd already folowed instruction from this forum in link http://forum.centos-webpanel.com/how-to/how-to-setup-thunderbird-and-outlook-mail-client-setup/

but it does'not worked ..

Pls Help me, if you experience with this and solved this problem . thank you.