I'm currently experiencing very bad performance while iterating
through the mailitems in a folder. I have to do this to check some
values in a couple of my custom properties every time a user is
switching folders.
I have read a lot about the Items.SetColumns() method, but can't seem
to get it to work with my custom properties.
This method is supposed to cache the properties you want to use, so
Outlook doesn't need to open every property of every mailitem you
visit.

Examples of what I have tried:
items.SetColumns("Storage"); // where Storage is my custom property
items.SetColumns("http://schemas.microsoft/mapi/string/
{00020329-0000-0000-C000-000000000046}/Storage");
items.SetColumns("http://schemas.microsoft/mapi/id/{00020329-0000-0000-
C000-000000000046}/0x8020001E"); // 8020 is according to outlook spy
the tag for this property and 001E is the tag for STRING8
items.SetColumns("http://schemas.microsoft/mapi/proptag/0x8020001E");

In addition, I have tried every possible combination of the above,
with no luck...

Any suggestions!??

The method does work with EntryID, Subject and fields like that, but
not with my custom ones..

Any help would be appreciated