Outlook (desktop Classic) not updating Mess!!

Jennifer 100 Reputation points
2026-08-18T09:42:34.9833333+00:00

Hi Please help!

I use Outlook classic on a desktop in my office and I have it on my laptop at home.

Couple of weeks ago, syncing was taking ages on the desktop one (always when you need to send an email in a rush) It once said 79 hours!!!

So yesterday I searched and google AI came up with certain things to do, which I did but at one point all the folders disappeared. I rebooted and the folders came back but a lot of them are not updated for a couple of months when they definitely were and the Sent folder and some other folders are empty saying Nothing In Folder! but others are ok. I've clicked on Update folder, I've left the pc on for hours but no change.

I can send emails and receive with not issue.

I tried setting up a new profile with all the exact same details but it keeps coming up with 'the server has rejected your login' even though I've gone to my account online to accept the security notification as being me.

AI is now saying to delete the .ost file which may be corrupt and reopen outlook which will update all.

What are your thoughts?

Outlook | Windows | Classic Outlook for Windows | For business
Answer accepted by question author
Hani-Ng 1,220 Reputation points Independent Advisor
2026-08-18T10:06:24.12+00:00

Hi Jennifer

You can try AI's recommendations first, as rebuilding the OST cache is a logical next step given the symptoms you've described.

Regarding your concern about the OST file, if the missing emails and folders are still visible in Outlook on the web, then rebuilding the OST cache is generally a reasonable and safe troubleshooting step. The OST file is simply a local cache of your mailbox, so Outlook can generate a new one and re-download the mailbox contents from the server. I would suggest renaming the OST file first rather than permanently deleting it.

Before doing that, I'd recommend signing in to Outlook on the web and checking whether the folders that appear empty in Classic Outlook (such as Sent Items) contain the expected messages. If they do, that would indicate the mailbox itself is healthy and the issue is likely local to Outlook on this PC.

You can also check the Mail to keep offline setting under File > Account Settings > Account Settings > Double-click the account. Make sure the slider has not been changed to store only a limited period of mail, as this can sometimes make folders appear incomplete.

Given that Outlook can still send and receive messages, but some folders are showing outdated or empty content, a local synchronization issue involving the OST file remains a possible cause.

Additionally, in a Microsoft 365/Exchange mailbox, Outlook typically manages folder synchronization automatically. Combined with the symptoms you've described, the greyed-out folder options may be another sign that Outlook is experiencing a synchronization or local cache issue.

Since this is a business account (based on your thread's tag), I would also recommend contacting your organization's IT administrator or Microsoft 365 administrator regarding the "server has rejected your login" error when creating a new Outlook profile. They can check whether there are any authentication, Conditional Access, licensing, or mailbox-related issues that might be preventing Outlook from successfully connecting with a new profile.

I hope this information helps.

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  1. AI answer

    2026-08-18T09:42:56.11+00:00

    The next step is to rebuild the local Outlook cache by renaming the .ost file, then let Outlook resync the mailbox.

    1. Close Outlook completely.
    2. If a File is in use message appears while working with the data file, press Ctrl+Alt+Delete > Task Manager and confirm Outlook.exe and Winword.exe are not running. End those processes if they are still open.
    3. Rename the .ost file.
    4. Start Outlook again.
    5. Wait for the Preparing for first use message and allow the mailbox to fully synchronize. The time required depends on mailbox size.
    6. After sync completes, check whether the missing or empty folders now show the correct content.

    If the issue remains after the .ost rebuild, the local cache is not the cause. Then use this order:

    1. Start classic Outlook in safe mode to rule out an add-in problem:
      • Press the Windows key
      • Type outlook.exe /safe
      • Press Enter
      • If Outlook behaves correctly in safe mode, creating a new Outlook profile is the recommended next step.
    2. Create a new Outlook profile from Control Panel > Mail > Show Profiles > Add. After creating it, set Prompt for a profile to be used, then start Outlook and choose the new profile.
    3. Run the Inbox Repair Tool (SCANSPST.EXE) to repair Outlook data files.
    4. Repair the Outlook/Office installation. A repair can take up to about half an hour.

    Because some folders are showing Nothing In Folder while mail flow still works, this strongly points to a sync or local profile/cache problem rather than send/receive failure.

    For the new profile attempt that returns server has rejected your login, no supported fix for that specific sign-in rejection is provided here, so the safest supported path is to finish the .ost rebuild first, then test safe mode, then create a new profile again from Control Panel > Mail.

    AI-generated content may be incorrect. Read our transparency notes for more information.

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