Are there networks that are completely blocked for your services?

Yes!

There are a handful of networks that we have classified as pure spam operations and are completely blocked from sending to and from our services.

The ASN numbers of the networks that we have completely blocked are: 12695, 19531, 28098, 29182, 34665, 40065, 43811, 43830, 49392, 49870, 51447, 56485, 62212, 136647, 136800, 200019, 202306, 202468, 205090, 208911, 211237, 211252, 211619, 213035, 398646, 399471.

If you really want to exchange emails with someone using one of these networks, you need to use another email provider.