First of all, contact your e-mail provider and make sure their servers are working as expected. It could simply be that your provider has a temporary disturbance which prevents anyone, not just Spamdrain, from connecting to their servers.
If there are no disturbances at your provider, it could be that they are blocking our servers. Please ask them to make sure their firewall isn't blocking any of the following IP addresses:
188.8.131.52 - 184.108.40.206 (220.127.116.11/21)
18.104.22.168 - 22.214.171.124 (126.96.36.199/21)
188.8.131.52 - 184.108.40.206 (220.127.116.11/21)
18.104.22.168 - 22.214.171.124 (126.96.36.199/22)
188.8.131.52 - 184.108.40.206 (220.127.116.11/22)
18.104.22.168 - 22.214.171.124 (126.96.36.199/22)
188.8.131.52 - 184.108.40.206 (220.127.116.11/22)
18.104.22.168 - 22.214.171.124 (126.96.36.199/22)
Another reason of the issue could be is that your email provider allows only country specific connections or blocks connections from specific countries. If that is the case please make sure the connections from Germany, Finland and USA are allowed.
If this does not resolve the issue please contact Spamdrain support.