We have published free
mining pools whitelist which can also be used as a DNS record on your farm.
It will speed up the connection time to the pools and avoid some delays/errors on DNS.
Also if you have some blockages set up on the firewall or by ISP, you'll likely bypass even that.
msOS users already got this file implemented so it will get regularly updated automatically.
If you have some other OS, follow the instructions that you can find on the provided page.