This is the easiest one to find. There were many others but I think I accidentally deleted them. After this message is a bunch of jibbersh that I can't understand and I would post it but it contains very personal information.
*** ATTENTION ***
Your e-mail is being returned to you because there was a problem with its
delivery. The reason your mail is being returned to you is listed in the
section labeled: "----- The delivery status notification errors -----".
The line beginning with "Diagnostic-Code:" describes the specific reason
your e-mail could not be delivered. The following lines contains the
RFC822 header of the original email message.
Please direct further questions regarding this message to your e-mail
Well, in that case, there are a couple possibilities. One is that there's something wrong with your e-mail account.
The other, however, is that you have been blocked from sending e-mail messages to your doctor. If you've been sending a lot of messages to her as a substitute for making an appointment or scheduling a phone consultation (something that I can tell you most doctors would not welcome), then it may be that an e-mail filter has been set up and is bouncing your messages back.