Outlook for MAC - sent items disappeared

[KerryE]

I have an ongoing Office 365 subscription.
On my iMAC (High Sierra) I am using Outlook but suddenly all my sent items disappeared.

Recently our email server changed so I had to change the settings to make sure I could still send/receive from the Mac.
It looks like this somehow caused the damage! (or it could be a coincidence?). Anyway, all the old sent emails have disappeared.
However, when I now send an email from the Mac it does stay in the sent items.

I also changed the settings on my PC and that had no effect on the sent items on the PC.

Actually this iMac belongs to my better half, and she is not best pleased about losing the sent items emails, as so many were very important.

I am not really a Mac user so I do not know where to start with this 
Can anyone help please

[KerryE]

I know what has happened here...

On my PC outlook is set as a POP account.
On the iMac outlook is set as an IMAP account.

So since the server changed, everything on the iMac was lost 

I wish our provider had asked me the right questions when he said do I need any of the old emails!
Big lesson learnt here.

[Lisa_maree]

Thank you Kerry for posting the solution, good to know you sorted it