At the moment it appears we're seeing some users who have BT as their ISP not fully able to go to buffer.com.
As a workaround, we've discovered that switching your DNS servers of your computer to google's 18.104.22.168 server should fix things up.
Here are some quick steps to changing your DNS to 22.214.171.124
Windows: You can refer to this guide on changing DNS.
1. Head over to System Preferences
2. Select Network
3. Select Advanced
4. Select DNS
5. Hit the + button and enter 126.96.36.199
6. Hit ok, and head over to buffer.com.
This should fix things up, though please do reach out to us on twitter (@buffer) if you're still experiencing issues.