A delegate and a Manager have different policies set. Both policies have different disclaimers set using Explicit or Organizational Server Policies. When a delegate sends a message from a Manager's mail file, the delegate's disclaimer (under the delegate's server-based policy) is appended to the message.
it would be better to have the option for a dropdown "Disclaimer" selection based on the specific mailbox before sending the mail. In every company there are some functional mailboxes which need this. i.e. marketing, info, accounting