I'm replying to messages, but they are not being delivered to the recipient
Microsoft Outlook Mobile Services are specific to Outlook 2007 and later. Replying to a message from a non-Outlook email client means the message will not be delivered to the recipient. The reply must come from Outlook 2007 or later.
Further, if you send a message, receive a reply and then reply to the reply, the message will not be delivered. This is a limitation of the Microsoft Outlook Mobile Service. Rather than replying to a reply, you will need to send a new message to the recipient.