To unblock emails in Gmail, either find an email from the sender in your Spam folder and click the "Not spam" button, or go to Settings > See all settings > Filters and Blocked Addresses and find the sender in the "Blocked Addresses" list to unblock them. You should also check your filters, as an email might be getting blocked by a specific filter rule, and delete that rule if necessary. 

Method 1: Unblock from the Spam folder

  1. Open the email from the sender you want to unblock.
  2. Click the "Not spam" button at the top of the email. 

Method 2: Unblock through settings

  1. Click the Settings gear icon in the top right, then click See all settings.
  2. Go to the Filters and Blocked Addresses tab.
  3. Scroll down to the "Blocked Addresses" list.
  4. Find the email address you want to unblock, click Unblock next to it, and confirm in the pop-up window. 

Method 3: Delete a blocking filter

  1. Go to Settings > See all settings > Filters and Blocked Addresses.
  2. Find any filters that might be sending the sender's emails to trash or spam.
  3. Click Delete next to the filter and confirm.

Method 4: Add to Contacts

Adding a sender to your Google Contacts can help signal to Gmail that the sender is safe, making it less likely their emails will be marked as spam. 
  1. Go to Google Contacts on your computer or use the Contacts app on your mobile device.
  2. Click Create contact (or the plus sign in the app) and enter the sender's information, including their email address.
  3. Click Save.