version limitation for triggering my app and opening email attachment

I have used CFBundleDocumentTypes and ask system to trigger my app when I touch the email attachment file.

It worked on my iPhone, iPad, but it has no function on ipod (os 3.1.3). It only display the options 'Save Image' 'Copy' wh开发者_运维技巧en I touch and hold the email attachment file. If I select 'Copy' and paste it to app 'Note', it only display cid:**--*--*******

Does this function have version limitation ?

Welcome any comment

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CFBundleDocumentTypes is supported in iOS 3.2 and later and all versions of Mac OS X.

Document Support section in What's New in iOS 3.2 mentions it.