Steps Gmail not working in Outlook:

• In Gmail's settings, enable IMAP access.
• Log into your Gmail account and click the little gear in the upper right corner of the window to change your settings. Select View all options. Go to the Forwarding and POP/IMAP tab after that.
• Make sure that the IMAP Status is set to Enabled. POP, on the other hand, should be ignored. This one is really outdated, and no one should continue to use it.
• IMAP is a protocol for sending and receiving messages between a client and a mail server. It enables the server to sync your mailbox across all of your devices, ensuring that everything is up to current.

Read More: Can I connect Salesforce with Outlook 2007?