For some reason this particular postmark appear just far too often particularly in ebay but also elsewhere. Just a few days ago the $10 stamp on the left ended with a final price of $66. There are also $2 and $5 stamps bearing the same postmark and are still currently ongoing in ebay. Last week, another $5 stamp, also with the same postamark was sold for £26.

Curiously the postmark would only appear on the 1904-05 stamps issue with the 4 cents surcharge. I haven't seen the same date appear in any other North Borneo stamps issues.

The postmark is supposed to be the Sandakan D11, in use from 29.9.04 to 14.10.15. It is strange that within about 11 years of usage, 11 Aug 1905 seems to occur far more frequently than the whole 11 years usage combined.

Now look at your Sandakan D11, is it 11 AUG 1905?

Note: The Sandakan 11 AUG 1905 is now known to be a CTO instead of a fake cancel. Read more about it here.