OK: So this mail rationalising saga is throwing up all sorts of interesting behaviour, that has been fun to discover, but this latest one has me stumped. I had to regroup and rationalise my mail and folders after Google, passed virgin mail handling back to virgin. This meant gradually copying mail from the web folders to local folders. Virgin had duplicated the mail across several folders, and their dates overlapped, so, on download to local, there were many duplicates. I've been very grateful to have the 'Remove Duplicates' add on, without which, I would never have tried this. Today, I thought I had finally got the right method and had managed to weed out a few big files that were holding things up. Then I noticed, that, despite running Remove Duplicates methodically, on the local folders after each new download batch, I could see plenty of duplicates were not being picked out. The only thing different between each pair of unfound duplicates is the 'Order Received', but Remove Duplicates ignores this (It also ignores the source code headers: which change with each folder move). The weird (but useful) thing is: If I copy a local folder with duplicates in, to a new IMAP folder, Remove Duplicates finds them all! I cannot imagine what is hiding the differences when in a local folder. I use the same settings in Remove Duplicates for both, yet it finds loads in an IMAP folder, and none in a local folder! The only thing that looks different are the 'Order Received' numbers: In the local folders, a single folder can have several sequences of received numbers, and duplicates may have numbers many millions apart. Moving or copying to a new local folder doesn't change the received number. On the other hand, a new IMAP folder starts numbering again from scratch, so the duplicates get numbers much closer together than the ones in the local folders, But they are still different numbers, so, if it was the order received number causing the problem, then the duplicates shouldn't be detected in the IMAP folder either: but they are. What is going on? I've been puzzling over it for a couple of days. I've found a way round it (upload; remove dupes; download to new local folder), but why is it not detecting stuff in the local folders that looks identical? Many thanks to anyone who knows the answer! Cheers.