Spam filters not applied as email arrives
I've noticed an issue with the spam filters on my email over the last few months. I view my emails from Outlook 365 on my desktop and from Windows 10 mail on my mobile devices.
On my desktop, Outlook 365 downloads the messages to a local PST file when I check for messages. Once downloaded, they are always there as I would expect. Outlook 365 only downloads new messages. I do have junk email filters set up in Outlook 365 as well, which generally catches them. This is all as expected.
However, on my mobile devices, it appears that some messages I consider spam sit in my inbox for a while and later are correctly identified as spam. From my mobile device, if I leave them alone, they seem to eventually disappear as they are identified as spam by AT&T/Yahoo email. It seems like the spam filters only run periodically on what's in my inbox rather than as emails arrive.
What's going on here? All my apps and O/S's (Windows 10) are up to date and I have not made any changes to my email either on-line or my local apps.