I tried obtaining the reply to the mail by using RDOMail.Reply method. However, after inspecting the returned object, I've noticed that the signature is not part of the HTMLBody property, as it is when using method MailItem.Reply (which I'm not using because it throws 0x80004004 (E_ABORT) exception). Also, attachments that would be needed for the signature if it contains images are not preserved as they are with MailItem.Reply. I've tried applying the signature separately, using Signature object. This adds signature to the HTMLBody, but doesn't use the _MailAutoSig attribute to mark the signature part therefore if I select "Change signature" from Outlook Ribbon, signature doesn't get replaced because Outlook has no way of knowing it is a signature.
Is there a way to obtain reply from RDOMail that would contain signature Outlook knows how to replace?
var rdoMail = session.GetMessageFromID(entryid);
var reply = rdoMail.Reply();
reply.HTMLBody = "";
var Account = session.Accounts.GetOrder(rdoAccountCategory.acMail).Item(1);
var signature = Account.ReplySignature;
signature.ApplyTo(reply, false);
reply.Save();