Some email providers (typically school or business email) outsource spam checking to external companies. Some of these external companies can be heavy-handed when fighting spam, and collateral damage unfortunately happens - innocent parties such as AnkiWeb can end up get blocked when a different customer on the same network has sent inappropriate mail.
If you have access to an email address at another provider, the fastest solution is to use the Account tab of AnkiWeb to change to your other email address.
If you do not have access to another email address, you could try asking your email provider to remove 18.104.22.168 from the block list they are using. It is a dedicated IP used only by AnkiWeb, hosted in Amazon's network. If your email provider are not able to fix the problem for you, please sign up for a free email address at somewhere like gmail.com instead, as they reliably accept the email we send.