how do I allow an email address/domain that appears in spam to go to inbox
This depends on what moved the message to spam in the first place.
If it was your server, then you need to login to your webmail interface, and mark the message as not spam. Otherwise the server will just keep moving messages from that sender to spam.
If it was eM Client, because you added the address or domain to the Blacklist, then right-click on the message and choose Move to Inbox > Move to Inbox and remove blacklist…
Thank you. I followed your advice and it worked.