Blocking messages in Gmail sends emails from a specific address to your spam folder. If you need to unblock an address, the path is not so obvious. Let me show you three solutions.
two desktop solutions (PC and Mac)
one mobile solution (Android and iOS)
Unblocking from the email
Use this desktop method if you can find and open a previous message from the blocked sender. Use the search bar or check the spam folder.
Go to your Gmail account.
Open a message from the blocked sender.
Click Unblock sender.
Click Unblock in the confirmation popup.
If the message is in the spam folder, click the Report no spam button to move the message to your inbox.
Unblocking from the Settings
On your desktop:
Go to your Gmail account.
Click the gear icon at the top right corner of the page.
Click See all settings.
Click the Filters and Blocked Addresses tab at the top of the page.
Click the Unblock link.
Optionally, mass unblock email addresses by clicking Select: All at the bottom of the email list.
Unblocking on the Gmail App
Use this method on a mobile device.
Go to your Gmail app and sign in.
Look up an email from the blocked party in the search bar or check the spam folder.
Tap the Report not spam sender button on the greyed-out message.
You're all set.
Once you unblock an email address, you can start receiving messages from the sender.