if the pst is corrupt run scanpst.exe. As always first rule of diagnostics is reboot
Outlook has a mail logging option where you can view the “conversation” outlook has with the mail server. This might reveal the nature of your problem.
could be your internet company at fault. Comcast is good for screwing with email/pop/imap connections.
Get rid of Outlook and switch to a webmail service like everyone else is doing. Your mail will never again go missing.
Outlook is ancient history.
Is your mail service through Yahoo?
They have instituted some new security protocols
recently that do not play well with Outlook 2007.
I don’t think I’d blame Outlook 2007.
When Verizon had AOL host their email service recently. I had to go to the AOL site and register my Verizon account and then change server addresses and ports before it would let me get my email.
But, it’s working fine now.
Check with your mail server’s website to see if they changed protocols
It’s been a long time since I used outlook 2007 but if I recall on 2010 and newer there is a item in your folder list (well below your inbox and sent items) that you can expand to view Sync Issue, and there you can see the more specific reasons you are not connecting to your mail server
https://support.microsoft.com/en-us/help/272227/how-to-repair-your-outlook-personal-folder-file-.pst
I had a problem with outlook 2007. It started downloading emails continuously, and downloaded each on hundreds, maybe thousands of times, so I shut off the email function and use the web page of the email server.
Did you install that Windows 10 Creators Update ? I have a few old Dells and it kills their internet ,Wifi and Wired and I bet it kills other things
if you have Webroot for security, they had a MAJOR screw up today
Switch to Thunderbird - will do most of what Outlook does and will also keep working.