Unable to setup SMTP for multiple email domains

Your software
My Mautic version is: 4.4
My PHP version is: 7.4
My Database type and version is: MySQL

We currently have three domains in our organization, and we use Gmail for SMTP for all these domains. I have set up the Mautic multi-plugin, and it’s working perfectly. However, I’m having trouble setting up SMTP for all owners with different domains. I generated an app password in Gmail for a specific email and entered the details in the Configuration → Email Settings, and the test emails are going out successfully. But, when the user tries to send an email, it doesn’t go through. Can you please assist me with how to handle this setup issue?