Hi Sven,
I have been using archivemail since March 2003, always with compression. My configuration generates a new gzipped archive for every month for every IMAP folder. To give you some peace of mind, I just did a simple decompression test of all archives [~5000 right now] (gunzip $file > /dev/null) to check for errors and found none. Whatever error you have, I don't think archivemail is the culprit creating them.
Well thanks for your checks.It seems that I have to dig into this problem more thoroughly.
If I find anything that could be useful, I'll post here. Thanks again. Best, Steve