To migrate your Office 365 mailbox to Gmail, you first need to enable IMAP access in your Gmail settings. This allows Gmail to connect and fetch emails from your Office 365 account. Next, in Gmail, go to the “Accounts and Import” section and add your Office 365 email as a mail account using the IMAP server details. Once connected, Gmail will start importing your emails from Office 365 into your Gmail inbox. This process can take some time depending on the size of your mailbox.