Outlook is unable to send an encrypted email to recipients in my company

When sending S/MIME encrypted emails within Your Company with Outlook searches Your Outlook the public Recipient keys in the Global Address List (GAL ) .
Therefore, the administrator of your Company ensure that all corporate users her valid S/MIME certificates in the Active Directory (AD) and/ or Azure Active Directory (AAD) registered have .

AD/AAD synchronized By default, the email addresses and S/MIME certificate details are updated every 30 minutes with the GAL.

While Outlook for Mobile always performs a live search in the connected GAL , searches Outlook for Windows and Outlook for Mac by default in the Offline Global Address List .

The offline GAL will once every 24 hours created , based on dem last successful Synchronize the offline GAL with AD/AAD.
Therefore When using the standard automated Processes and the client ‘s online connection up to 48 hours take until the offline GAL synchronizes is and the latest S/MIME certificates other user in the Companies available in Outlook are .

To synchronize Your offline GAL for Outlook for Mac or Windows manually to force :

1. Go to the Send/Receive tab in the Ribbon.
2. Click Send /Receive Groups .
3. Select Download Address Book .
4. Click OK .

To synchronize from AD to AAD manually to force :

1. As an administrator, open PowerShell on the AD that has AD Sync executes .
2. Lead You the following command out of :
   Start ADSyncSyncCycle – PolicyType Delta

To synchronize from AD to GAL for Your local Exchange server manually to force :

1. As an administrator, open PowerShell on the AD.
2. Lead the following command out of :

Update- GlobalAddressList -Confirm

Sources:

• https://docs.microsoft.com/en-us/powershell/module/exchange/update-globaladdresslist?view=exchange-ps
• https://support.microsoft.com/en-us/topic/administering-the-offline-address-book-in-outlook-51958cc8-684a-83f9-aea5-97d4dddc0af4