Outlook IMAP & Optimum Server - 6 Duplicates of each email - How to Stop Duplicates

Question

Hi.

I just got a new computer and am setting up my email account in Outlook 2016. I re-installed Office and Outlook on the new machine. I set my Outlook account as IMAP with optimum as my internet provider (mail.optonline.net) with the port # and SSL. I also imported my .pst file from the older machine.

Then, I received an email from Opt. that my storage was full. When I signed-in to Optimum email, there were 3-6 duplicates of each email. I spent a few hours deleting stuff on Opt. so I would have some free space. When I went back into Outlook, and hit the send/receive button, the storage was then full gain on Opt. in like a split second. There are no duplicates in Outlook. It seems to possibly be a syncing problem?

I also have this email setup on my ipad and iphone. It seems to affect the iphone not the ipad. The phone has 1,000s of “new” messages.

My Question is, can I:

Delete all the emails on the optimum server so I have 100% free storage.

Uninstall and reinstall Outlook.

Import the .pst file

Configure it for IMAP.

Or will this still result in duplicates on Opt. server?

Trying to figure the quickest way to fix it, so I prevent duplicates on the Opt. server, especially after I open Outlook.

I need the emails and have made a few back-up .pst files on different drives, to be safe. I would not need these files to be on Opt. server, if I have copies in Outlook.

Any help is greatly appreciated. Thanks so much.