Go to your Google Account page
Navigate to: https://myaccount.google.com/
Go to the App Passwords section
Click Security menu item in the left sidebar
Scroll to the Signing in to Google panel and click App password
Note: The App Passwords section is available only if you have Two-Step Verification enabled on your account. Please make sure it's enabled before proceeding. Two-Step Verification is a recommended practice to secure your account.
Create an App password for Prezly
On the App passwords page, open the Select app drop-down and choose Mail
Choose Other In the Select Device drop-down
And type Prezly Mailbox Sync into the text field appeared
Click Generate and copy the given password (4 groups of characters in the yellow box).
Use the password to connect your mailbox in Prezly
Now input the password in Prezly in the Connect mailbox page.