Forum Discussion
mail@mydomain is causing a cert mismatch error in all browsers for Outlook.com
Hi Niko,
That is what I was thinking.
It's just strange that we have had an influx of calls about it, and I wondered if it had been working before, since I couldn't see how.
I will look into the methods you mentioned to see if I can do anything to help them.
But for now, I am just telling them to go to outlook.com
Thanks
Midi
It's entirely possible that mail.mycustomdomain.com worked at some point in the past — perhaps because an on-premises Exchange server or a reverse proxy was handling the certificate for that hostname, and after a migration the record was inadvertently left as a plain CNAME. That could certainly explain the recent increase in support calls.
In the meantime, I’d recommend giving users the following address for webmail:
Rather than directing them to outlook.com, I would suggest using the dedicated Microsoft 365 work/school URL.
outlook.com is primarily intended for personal consumer accounts (Outlook.com/Hotmail). While Microsoft's sign-in page can sometimes detect a work account and redirect to the Office 365 portal, that behavior isn't guaranteed and can cause confusion — especially for users who also have personal Microsoft accounts.
A better approach is to provide the proper Exchange Online webmail address:
- https://outlook.office.com/owa/
or simply - https://outlook.office.com (which will automatically redirect to the correct OWA page)
This is the documented and supportable URL for Microsoft 365 business and school mailboxes. Users can bookmark it and sign in with their work email address (email address removed for privacy reasons) as usual.
In short, I’d recommend sharing outlook.office.com as a temporary, reliable link while you explore setting up a proper redirect from mail.mycustomdomain.com.