Error Configuring Some MAPI Accounts in Outlook
Problem reported by Bruno Gomes - 9/2/2025 at 3:08 AM
Submitted
Hi,
We have some accounts that we can't configure in Outlook using the MAPI protocol. The account is configured, but when we open Outlook, we always get the error: "The set of folders cannot be opened." 
Has anyone experienced this and know how to resolve it?

Thanks

Use cached exchange mode. You forget to set that during initial installation of the account.
Bruno Gomes Replied
I have already had this option active for 1 year.
For every account you install??
Bruno Gomes Replied
Yes Brian
Kyle Kerst Replied
Employee Post
Hi Bruno, sorry to hear you're having trouble with this. More often than not when I see this error there is usually a DNS or other connectivity issue preventing Outlook from reaching the MAPI endpoint. A good way to check is to check the following items from the affected computer: 

- Does https://mail.customer-domain.com resolve properly and without SSL errors in a browser?
- Does https://autodiscover.customer-domain.com resolve properly and without SSL errors in a browser?
- Can the affected PC successfully complete an SRV lookup for _autodiscover._tcp.customer-domain.com? It should return mail.customer-domain.com on port 443

If any of the above fail you can try adjusting local DNS on the client machine and flushing caches before trying again. SSL errors will need to be corrected for any of the noted URLs above as well (tailoring for your customer domain.) Beyond that, installing something like Fiddler Web Debugger Classic and configuring it to decrypt HTTPS traffic before allowing it to monitor Outlook startup may also provide some clues here. 
Kyle Kerst Acting IT Manager SmarterTools Inc. www.smartertools.com

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