Problem
You are using Signature 365 server side signatures to send an email to a recipient on your domain but email content such as tasks, contacts and voting buttons are removed from these emails.
Cause
Outlook utilizes a proprietary Microsoft data format called TNEF (Transport Neutral Encapsulation Format) to enable Outlook specific features. When sending email outside your domain, its cannot be guaranteed that other mail clients support this format.
To prevent compatibility or display issues in these clients, emails leaving a Microsoft 365 Tenant have these features removed to prevent these issues.
As Signature 365 uses an external connector to inject signatures into your emails, these features are removed when the service is used.
Solution
To resolve this, you can create a remote domain through the Exchange admin center or using Powershell, and set it to allow TNEF for this domain.
Information
You can choose either of the following methods to enable this feature.
Logon to your Microsoft Tenant by navigating to https://admin.exchange.microsoft.com/#/remotedomains.
Click the + Add a remote domain button.
In the New remote domain window, name the new remote domain - we suggest "Internal" or similar. The remote domain will be your email domain name.
Leave the Email reply types as Allow only external and the Automatic replies settings as shown, and click Next.
Leave the Message reporting settings as shown and click Next.
Set the Use rich-text format radio button to Always, the supported character set dropdowns to Unicode (UTF-8) and click Next.
Review the settings and click Save.
If you are using additional domains that receive email, they will also need to be added as remote domains in the same manner.
Confirm that the setting has applied and is working by sending an email containing a Task / Contact or similar to an internal recipient.
Connect to Exchange powershell.
Import-Module ExchangeOnlineManagement
Connect-ExchangeOnline -UserPrincipalName {username}
Run the following commands to create the new Remote domain and enable TNEF.
New-RemoteDomain -DomainName "emaildomain.com" -Name "Internal"
Set-RemoteDomain -Identity "Internal" -TNEFenabled $true
Confirm that the setting has applied and is working by sending an email containing a Task / Contact or similar to an internal recipient.