RSSCategory: New Outlook

Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened

| May 7, 2026

Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened

This can be a snaggy error to fix. I have seen this error for years with Microsoft Exchange. Lately the fix for me has been to delete the 16,454 KB size file in the app data folder.

Usually I back up any file I delete but this one is not really a data file that works with the OST, when you set up new Outlook profile it just makes it. And this can get snagged up I believe.  If you delete it, then try reopening Outlook it might work. If not make a new profile (don’t delete the old one), set Outlook to open new profile. See if it performs better.

I also had to run 365 updates on my last client to get it working.

If not, then you might have other issues such as a VPN problem, Antivirus or Firewall.

If you need help, please use the form below.

Why is Outlook Slow to Sync

| May 4, 2026

Why is Outlook Slow to Sync

Outlook Classic can be slow to synch for many reasons, below are the top things I look for when I help a client. As an expert in Outlook Classic, I go through most of these during the onboarding of our first appointment and can figure out the problem quickly. Then we move on to solutions. Solutions may take time to repair, or can be moved to a project (migrate email to Exchange) or repair with other options. All options are your choice. If you need help with Outlook slow to sync, feel free to use the form at the bottom of this page and contact me.

  • VPN interference
  • Antivirus or security software (Malwarebytes, Norton, etc.)
  • Large OST file (cached mailbox too big)
  • “Download Shared Folders” enabled
  • Too many shared mailboxes
  • Poor or high-latency internet connection
  • Exchange Online throttling (Microsoft 365 limits)
  • Corrupt OST file
  • Problematic Outlook add-ins
  • Corrupt Outlook profile
  • AutoDiscover configuration issues
  • DNS misconfiguration or slow DNS resolution
  • Cached Exchange Mode disabled (online mode)
  • Windows Search indexing problems
  • Background apps consuming bandwidth (Teams, OneDrive, backups)
  • OneDrive sync conflicts (especially with PST files)
  • Too many items in a single folder (large mailbox folders)
  • IMAP account limitations (non-Exchange accounts)
  • Firewall or network filtering / deep packet inspection
  • Outdated Outlook or Windows version

iCloud for Windows not synching with New Outlook

| April 29, 2026

iCloud for Windows not synching with New Outlook

If you have iCloud for Windows set up in New Outlook, you might notice a synching delay. I just helped a client who called me back to let me know about this. I told him that iCloud on the browser and phone update automatically but there might be a delay for New Outlook to sync up. There are no options that I know of to sync it faster, so expect up to 15 minutes.

I’m not sure if this is typical as I have helped many people with iCloud and New Outlook and no one else has reported this delay, but it could be a recent change so that’s why I created this post.

If you need help with connecting your iCloud for Windows with Outlook Classic or New Outlook, please use the form below to get in contact.