iPhone can't seem to read or download an email sent from a Windows service with an attachment and keeps cycling through this non-state until you delete the email via another means.
At work we have a Windows service that does some data collection on daily business within our office (the software itself has been written in C# using Visual Studio 2008) it then generates a simple email, adds an Excel 2003 attachment to that email and sends it to a list of users.
The problem comes when anyone tries to get mail on their iPhone or iPad, the mail app does the usual process of checking for email and chiming to indicate new mail, but when you view the inbox where the email should be it briefly appears and then disappears over and over. As it is doing this the bottom of the Mail app is saying "downloading 1 of 1 message", then it flicks to the updated status then back to "downloading 1 of 1 messages", until you kill the app it will keep doing this all the time other email arrives fine into the same account however.
If the user then views their email account on the laptop or desktop all the email including this one downloads successfully and poses no problems, however even after receiving the email on a laptop etc. the iPhone/iPad will still continue this cycle, only when you delete the email from the account does it stop the Apple device from going crazy.
The mail accounts are hosted on an internal mail server which is not Exchange, all the accounts are IMAP we do not use POP3 for email delivery.
The only thing we have noticed is that if we change the code in the Windows service so that it does not put an attachment onto the email but just send a simple email the email downloads perfectly fine to the iPhone/iPad with no issues.
Neither the attachment or the email itself have any sort of unusual or extended characters in them.