Remember, if you send an attachment which has a specific program requirement for opening, then the receiver must also have that specific program.. Right now, something that comes to mind is the newest version of Microsoft Word, Excel, or Powerpoint.. If you've got Word 2007 and you send it to a user which does not have that version, they won't be able to open it unless they install the new Office 2007 compatibility pack.
The same thing applies with other attachments and associated programs as well.
HOpe this helps.
Grif
I often forward Yahoo emails, with attachments(sent by friends),to other members of the family.They are each using XP while I have Vista Home Premium.They are unable to open the attachments included with the forwarded emails.Does anyone have any ideas about what is happening? Apart from this,I'm enjoying my new computer and Vista.

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