Voting button in email does not show up or work with external exchange users

Voting button not visible to external exchange users in the email

Note: For the voting option to work email should go out as Rich text format.

Resolutions: To solve this issue, follow the below steps.

Create a new remote domain for the partner
New-RemoteDomain -Name partner domain -DomainName

Once the remote domain is setup Open remote domain properties, Select "Message Format" under the "Exchange Rich-text format:" select "Always Use" and save the settings.