Q: I send an e-mail message from my iPhone 5c and it shows up in Sent folder as a duplicate, 2 of the same e-mail messages sent at the same time.

Did the mail get sent? Is the only issue the fact that it appears twice in the Sent folder?

I have the same issue on my iPad. Yes, only one e-mail gets sent to the adressee

Do you happen to have "Always Bcc Myself" turned on?

Thanks for the tip. I now understand that this must be a Hotmail problem, as I discovered I encountered it on the PC as well. But I looked for the "Always Bcc Myself" menu alternative in Hotmail but couldn't find it. Does your wisdom extend to that as well?

The setting I was referring to is in Settings>Mail, Contacts, Calendars. It is a global setting.

No, that setting was not in use on the iPad

Then as you said, this could be a Hotmail issue, and I'm sorry but I am not familiar with any settings with that particular provider.