Open your ONLYOFFICE Groups portal in a web browser. Sign in to the portal using your administrator or owner account.
Go to the Settings section clicking the icon on the top, select the Integration section in the left-side menu and switch to the Mail Server page.
In the Mail Server IP field, specify the IP address of the machine where ONLYOFFICE Mail is installed.
If you have changed the database access password at the previous step, click the Show Advanced Settings link to expand the form where the default access settings are specified. In the Mail Server database password field, specify your new password for the mail_admin user instead of the default one.
Click the Connect button below to verify if all the parameters are set correctly. If the connection between ONLYOFFICE Mail and ONLYOFFICE Groups is successfully established, you will see the 'Successful connection' message.
Click the Save button to apply the settings.
That's all. Now you can click the Configure Mail Server link that appears to go to the ONLYOFFICE Mail module. Follow the instructions provided here to connect your mail domain, create a new mailbox and check if the ONLYOFFICE Mail works correctly.