So, you opened your Gmail account, thought you were getting spammed, and blocked the email address. Now, you need to unblock that address. Unblocking is really simple, but the starting point isn't obvious. Here are three options that work on desktops and mobile devices.
Unblocking inside the message
Use this desktop method if you can open an old message from the blocked sender. Check the Gmail spam folder first, or use the search bar.
Open a message from the blocked sender.
Click Unblock sender.
Click Unblock in the confirmation popup.
Unblocking from the Settings page
Open your Gmail account on a desktop
Click the gear icon in the top right corner.
Click See all settings.
Click the Filters and Blocked Addresses tab at the top of the page.
Click the Unblock link.
You could mass unblock a bunch of email addresses. Click Select: All.
Unblocking via the Gmail App
Try this on a mobile device.
Go to the spam folder and look for a message from the blocked sender, or try the search bar.
Tap the Report not spam sender button on the greyed-out message.
After you unblock, you can receive messages from the sender.