Something else to consider is that iOS now has a combined inbox that shows all of the e-mail messages from all of the accounts on the device in a unified display. The one downside here is that when you go to compose a message and you are in that combined view, it defaults to whatever the default mail account is to send the new message. This may not be the user's traveler based account. Also, if the user has wi-fi active, have them shut off their wi-fi connection and see if it works using just the mobile connection. It may be that the wi-fi they are on is blocking access to the traveler server. Of course these are basic troubleshooting issues and I am sure you have already done them, but I just know that the unified inbox has snagged me a couple times.