Cannot see received mail after migrating account to new mac

I bought a new Mac Pro and migrated my user account from my old mac to my new mac pro using the migration assistant.

When I open mail I can see my mail folders and all the mails I received before the migration.

I can connect to my mail account and I can see new mail being received in the connection window.

However once this new mail has been received I do not see it in any of my mailboxes. I have no idea where it is or how to make it show up.

Thank you for your help.