I google and several article/forum writing that need to flush dns cache and also about several YM server cannot be accessed from Pidgin.

I try my friend advice to change YM server configuration to IP rather than domain name.
And it’s worked..
You will need to use cn.scs.msg.yahoo.com as Pager server since June 24, or you can update to pidgin 2.5.7 to solve this problem

Some people are reporting changing the Pager server didn’t solve the problem, you can follow these instruction to update your pidgin to latest version (for Ubuntu) : Updating Pidgin to latest version in Ubuntu

The steps: 1. Select menu Accounts – Manage Accounts

2. Select your Yahoo Messenger account & click ‘modify’

3. Select advanced tab

4. Change your pager server to : cn.scs.msg.yahoo.com

5. Then disabled & enabled your account. Or restart the pidgin.

And your Pidgin should able connect to YM

*Update*
List IPs can be used (thanks to Med):
66.163.181.179 – 66.163.181.180 – 66.163.181.181 – 66.163.181.182 – 66.163.181.183 – 66.163.181.166 – 66.163.181.167 – 66.163.181.168 – 66.163.181.169

Starting June 24 using IP doesn’t seems to work anymore, try to use : cn.scs.msg.yahoo.com

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