Outlook 2010 asking for all PSTs password when receiving a mail with read receipt request

Hi,<o:p></o:p>

I have 4 password protected PSTs. 3 of them are old, and just one is active (current mail archiving).<o:p></o:p>

When I open Outlook, as expected, it asks me for the password for the active PST. Thisisunderstandable.<o:p></o:p>

The weird thing is that, whenever I receive mail with read receipt request, when I open that e-mail, before opening it outlook
asks me for the passwords of all the other PSTs (the old ones). I don’t understand why.<o:p></o:p>

I checked my client rules, I don’t have any rule referencing the old PSTs.<o:p></o:p>

Thanks in advance.