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Yahoo is difficult to work with. Yahoo blocks certain IP addresses, and permanently rejects all email from those. This affects IP addresses that we use to host cryptoparty.org.
If you're interested in the details, you can read experiences with Yahoo's mail servers.
As a consequence, we have banned all email addresses from yahoo, ymail and rocketmail domains. If you attempt to use such an email address to subscribe to one of the cryptoparty.org mailing lists, you will get an error message saying the address is banned.
You should get an email address from any other place, to use it to subscribe.