It’s probably been said but it sounds exactly like one of the outlook clients was set up without checking the box that specifies whether the email is deleted on the server when a client downloads.
Let’s Emails 1, 2, and 3 are sitting on the server. Client A wakes up and says ‘oh time to download!” ... and downloads those mails. Let’s say this client A has been configured to NOT delete downloaded emails. So, emails 1, 2 and 3 are still sitting on the server. And ... email 4 arrives at the server.
Now email client B wakes up and says ‘Oh! Time to check for emails!’ .. and finds the 4 new (new to client B) emails on the server. It pulls them down. But alas, the little checkbox in the client’s configuration for that email account says ‘delete when downloaded.’
So ... bye bye 1, 2, 3, 4 on the server.
Now client C wakes up, checks. Nothing there.
All 3 clents have checked for mail but:
Client A only has and will only ever have 1, 2, 3.
Client B has all 4.
Client C will never see 1, 2, 3, 4. It checked too late to see they had ever arrived, and now they are deleted because of B’s configuration.
So, if you haven’t already -> go to the account configuration for each the email account (the one that’s been receiving all the emails is going to be the evil one, unless 2 of them are)... one of the tabs/options will allow you to either leave emails on the server after download, or discard them.
That may not be it, but it’s extremely likely given what you’re experiencing.
Good luck. If that’s what’s up, and you need all those emails to be recovered/present on ALL clients after you fix it, forward all the ones in question to yourself at that email, then they will all download (albeit as forwarded emails.) At least you’ll have all the original message content on all computers.
This is good to know, thank you!
Like your tagline.
The setup I use is: all but one of my computers/devices use IMAP only, and thus they never download or delete desirable mail from the server. They only view. I can use them to delete spam, and of course they can send, but they all always "leave messages on server" unequivocally.
One computer, my home desktop, is set to POP3, and it downloads the messages from the server. HOWEVER, it leaves them on the server for 60 days before deleting them from the server. That means that all my other IMAP clients have two months of "message history" always available.
Finally, on ALL machines, whenever I send a message, I include a BCC (blind carbon copy) to myself. This comes back around into the inbox, so that all the other clients will see a copy of the sent message. I use a filter to move the BCC copies into the Sent folder on the server. Then every client sees a coherent, complete picture of what has been received and sent.
I've been doing email since the mid-80's. This is the only sane way I have found to deal with a home desktop, a work desktop, two laptops, a phone, and a tablet.
Thank you again for your great explanation of the problem!