Improve Outlook 2016 IMAP Performance

If you're struggling with Outlook's performance when connecting to your mailbox via IMAP, the below options should improve the experience considerably.

The goals with the settings below are to:

Configure Outlook to keep complete copies of messages on your computer.
Configure Outlook to send/receive messages more frequently.
Run Outlook in off-line mode, so that it does not try to contact the server whenever you click on a message.

Follow the steps below. Note that depending on how you've customised Outlook, the various tabs may be different; so search for those settings, if not obvious.

On the Send/Receive tab, in the Send & Receive group, choose Send/Receive Groups
In the Send/Receive Group list, choose Define Send/Receive Groups
Select All Accounts
Change Schedule an automatic Send/Receive every to 2 minutes for BOTH on-line & off-line mode
Click the Edit button on the right.
A new window appears.
In the Accounts column, select your IMAP email account.
Select Download complete item including attachments for ALL folders.
Select BOTH Send mail items AND Receive mail items.
Access the Preferences group on the Send/Receive tab and press the Work Offline button.