When you subscribe to an RSS Feed, Outlook periodically checks for updated postings.
This is called the Offline Address Book and is being generated on the Exchange server.
Important: Some publishers strictly enforce these limits.
If you check for updates more frequently than the specified limit, the RSS Feed publisher can temporarily or permanently block your access.
Due to various synching schedules, it can take up to 48 hours before you could actually see a change in Outlook after a modification has been made on the Exchange server or in Active Directory.
In this guide, the relevant timings are explained and instructions are given in how you can directly force an update and resync, which can be very handy when troubleshooting or when you work in an Exchange environment which sees a lot of user mailbox mutations.