Some Microsoft 365 users might see a problem with receiving their inbound emails in LiveAgent due to a Microsoft's security initiative. When your Microsoft 365 mail account tries to forward your email to your LiveAgent's built-in mail account, instead of a new ticket, you'll get a bounce notification with the following text:
550 5.7.520 Access denied, Your organization does not allow external forwarding. Please contact your administrator for further assistance. AS(7555)
Please contact your Microsoft 365 administrator and ask them to allow automatic external forwarding for any mailboxes you want to connect with LiveAgent using the Forwarding option. This guide should help your administrators find and change the protection policy that is blocking the forwarding. Microsoft's documentation on these settings is found here: Configure email forwarding for a mailbox in Exchange Online.
Now you should be able to use the Forwarding option with your Microsoft 365 mailboxes however if it still shouldn't work then there still might be other transport rules or spam policies in place at Microsoft 365 that block external forwarding. If automatic external forwarding is still blocked after adjusting the policies covered about, you should contact Microsoft 365 support for assistance in finding any further blocking that has been set up in your Microsoft 365 account.