How to Configure S/MIME in Office 365

JohnVolmer  I am also looking forward to Mircosoft enabling this feature in Outlook for Mac. However, I think there is a technical constraint since the Certificate is stored in the KeyChain and Microsoft has to Publish it by picking it from the KeyChain. 

As an alternative, I am currently publishing the Public certificates of users manually to GAL. 

1. Install the SMIME Certificate on the User's Mac

2. Export the Public key/certificate in *.cer format from KeyChain

3. Publish it to GAL using PowerShell. 

Below are the commands to Publish a Public certificate to GAL. 

$cert1 = New-Object System.Security.Cryptography.X509Certificates.X509Certificate "C:\Users\Amit\Desktop\SMIME\SMIME_Public_Certificate.cer"
 
$certarray = New-Object system.collections.arraylist
 
$certarray.insert(0,$cert1.getrawcertdata())
 
Set-Mailbox -Identity email address removed for privacy reasons -UserCertificate $certarray -UserSmimeCertificate $certarray
 

To view the Published certificates. 

Get-Mailbox | ? {$_.UserSMimeCertificate -or $_.UserCertificate} | select Name,UserSMimeCertificate,UserCertificate 

Hope this will help. 

Also, please post here if there is any other effective method to Publish the Certificates to GAL. 

Thanks!