A secure connection cannot be established with the server <domain.com> because its intermediate or root certificate cannot be found. Do you want to continue?
You use Microsoft Outlook 2016 for Mac or Outlook for Mac 2011 to connect to a mailbox on a Microsoft Exchange server. When you send an email message that contains a large attachment, you receive the following error messages in Outlook for Mac.
If you continue, the information that you view and send will be encrypted, but will not be secure.
Microsoft has a suggestion for fixing this, issue a new certificate with the domain added as a SAN (subject alternative name) or just accept the wrong cert. But I bet you actually have a certificate for the domain name you have Office 365 or Exchange setup on, so why not use it? Here’s how.
- You need to track down where the domain is pointing to determine where the certificate needs to be installed. You may or may not know this, and I understand because like many of you I am a sys admin that takes over control of already existing systems. Just ping the domain name in the certificate warning (the <domain.com> bit, replace that with the domain in your warning). That will give you an IP, now track that IP to whatever web server, load balancer, or firewall it may be.
- Get your certificate ready. I work with Microsoft and IIS nearly exclusively so I have a handy PFX (certificate + private key, don’t let this out of your sight). Simply install that certificate to wherever that IP address is terminating. When Outlook resolves the domain name it will try and pull the cert from that device/server.
In my case the server was a reverse proxy load balancer, running ARR, IIS, and network load balancer. With ARR I have SSL offloading enabled so the certificate actually comes from this load balancer, not the web server. I added a binding to the site in IIS with the cert and the warning went away.
Outlook For Mac Attachments Warning 2017
More Solutions to Fix Cannot Open Attachments in Outlook 2016/2013/2010. If you still cannot open your attachments even after the solutions above, you have to resort to the ultimate solution, which is the use of a third-party repair software for corrupt.pst file. There is a possibility of a synchronization problem in MS Outlook and the attachment may get stuck midway. Therefore, to fix this Outlook for Mac unable to download attachments error, follow the step by step procedure given below: Choose the navigation pane and right-click on the account. Next click on the Properties option.
Symptoms
View Attachment Outlook
In Outlook 2011 for Mac, the status bar displays the following message:
Inbox: Downloading Attachments
The status shows 1/20, and after 20/20 is reached, the status returns to 1/20, and the process is repeated. You may notice this behavior if you recently configured a new Outlook Identity, a new account, or emptied the cache of a folder, and Outlook is synchronizing the data from the server.
Outlook Opening Mail Attachment Warning
Cause
Outlook Open Attachment
This behavior is by design. When Outlook 2011 for Mac downloads data from the server, Outlook first downloads the email headers and message bodies, and then Outlook downloads the attachments for each folder in batches of 20. During this time, the status displays Inbox: Downloading Attachments x/20. Then, the number repeats from 1 to 20 until all the attachments are downloaded.
Outlook 2013 Attachment Security Warning
Resolution
Outlook Attachment Security Warning
Allow for enough time for Outlook to finish synchronizing and downloading all attachments. If you have many items that contain attachments in the folder, this process takes longer.