dsync duplicating identical messages

[Bruno Viaris]

Dear list,

I’m trying to setup dovecot/postfix/getmail for a single user
application: I have 3 email accounts and 2 main computers (home and
work). I want to have an imap server on each machine with
sync/replication so that read/reply/delete status and sorting into
folders are identical. This part is achieved via dsync and seems to work.

Messages are fetched from my ISPs with getmail on both machines. The
problem I have is that dsync does not see that a message already fetched
on both sides is identical, and duplicates it.

I use sdbox (because I like the compression option and the separate
storage of attachments). The content of the messages (headers and body)
are identical, but the sdbox files have differences in the header and/or
trailer. In fact, for each incoming message, I get 4 slightly different
files (2 on each machine).

Do you know where I could find documentation on how dsync compares
messages, and also on sdbox file format ?

If you explain me that there is no way to prevent this duplication and
that anyway dsync does the right thing, I will probably use getmail only
on one machine and let dsync propagate the messages to the other site,
but I will miss the redundancy (and some speed) of my wished setup...

Thanks

-- Bruno

P.S. : Background:
Home has DSL with 10 MBit/s down and 1 MBit/s up, and full control over
NAT / firewall
Work internet access is limited by the 100 MBit LAN and has strict
firewall and complicated VPN.
So it is not easy for my home email client to access the imap server of
my work machine, and it is slow for my work email client to access my
home imap server.
I don’t trust any company for archiving my emails.