Using Exclaimer Cloud - Signatures for Office 365, voting buttons are not present in messages which are sent to a group.
Voting functionality is stored in a TNEF MAPI property. When a message is addressed to a group and routed via a send connector, it undergoes content conversion to MIME. However, the MIME format does not preserve the TNEF MAPI property, so voting buttons are not displayed.
When composing an email which will be sent to a group and requires voting functionality, add the group as normal but then expand it, so the message is addressed to individuals instead of the group.
We are investigating the issue with Microsoft to identify other possible solutions.