Security researcher Andreas Kurtz wrote a blog post in late April noting that iOS 7 does not actually encrypt email attachments from the Mail app, as Apple claims.
The issue reportedly remains in the current iOS 7.1.1.
Kurtz was told by Apple that the company was aware of the issue, “but did not state any date when a fix is to be expected.” It’s possible a patch will be issued in the near future, but for now, it’s advisable to send sensitive files using other, more secure means.