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.
The MIME conversion does not occur when an email is sent only to individual recipients. Therefore, expand all groups (including any nested groups) until only individual recipients are detailed in To, Cc and/or Bcc fields.