When I bought my laptop it came with Office 365 and I setup Outlook 2013 (365) as normal. I wasn't using Outlook on the website. But the 365 was a trial and I had my version of Office 2013 which I installed when the trial expired.
I had a terrible time installing Outlook 2013 because it kept telling me there were no data files. I tried to enter the data files manually in the Account setup, but it wouldn't accept them.
Honestly, I don't remember how I finally got Outlook to accept my .ost files, but I was stuck using those as data files. I think I said they were Outlook Exchange data files at one time, and that's what allowed my .ost files to be used. I had several problems with Outlook, and at the time I posted on some forums and was told by many people my problems were from the .ost files.
A few suggestions were made on how to convert them, but not much encouragement was given - saying it doesn't work well or it doesn't work at all.
My desktop - while I was using the laptop - had a disk die and it took 2 months to get it replaced. A two month old Western Digital Sata III drive. I will never buy another one of their products. Terrible support service.
Anyway, I just installed Office 2013, setting up as IMAP for my gmail accounts (just as I had on my laptop). The data files that Outlook created are .ost files. I couldn't believe it.
The laptop and desktop are not tied together in any way yet. But I was just certain if I installed Outlook 2013 with IMAP settings and a fresh start ( no Office 365) that my data files would be .pst.
Can anybody explain why they are .ost files? I don't want .ost data files!!
I've had so many problems on the laptop, I don't want those same problems here on my desktop.
I won't even go into the problems I've had. Right now I just want to pursue a way to get my data files to be .pst files. All of the email I care about is still in gmail, so I can easily delete the data files Outlook created and start over.
Please - if anybody has an idea, please share it. I'm desperate. It got so bad on the laptop I was using gmail on the web. And I do not like any web based email program.

I was a big Thunderbird fan for a while, but I have always really loved Outlook. And I want it back.....

Thanks in advance.