Larch is running on a third host with OpenBSD 5.1 amd64 and ruby 1.9.3.
When attempting to copy a folder from Maildir to Exchange larch will stop when it encounters large messages (around 10 megabytes?). Turning verbosity up to insane shows the following:
[10:51:52] [info] [>] copying uid 59: XXXXXXX - Training from HR Services
C: RUBY0090 CLOSE
S: RUBY0090 OK CLOSE completed.
[10:51:52] [debug] [>] Archives/01-2008-09: selecting mailbox
C: RUBY0091 SELECT Archives/01-2008-09
S: * 57 EXISTS
S: * 0 RECENT
S: * FLAGS (\Seen \Answered \Flagged \Deleted \Draft $MDNSent)
S: * OK [PERMANENTFLAGS (\Seen \Answered \Flagged \Deleted \Draft $MDNSent)] Permanent flags
S: * OK [UIDVALIDITY 253] UIDVALIDITY value
S: * OK [UIDNEXT 58] The next unique identifier value
S: RUBY0091 OK [READ-WRITE] SELECT completed.
[10:51:52] [debug] [>] Archives/01-2008-09: appending message: 09affe6e26b26eb11ef4ac6444d2d081
[10:51:52] [warning] [>] Archives/01-2008-09: flag not supported on destination: $Forwarded
C: RUBY0092 APPEND Archives/01-2008-09 (\Seen $MDNSent) "29-Jul-2009 16:39:35 +0000" {11957029}
S: RUBY0092 BAD Command Argument Error. 11
Larch will wait here for 30 minutes (the Exchange connection timeout value) and the attempt to copy the message 2 more times before giving up.
Any ideas? Thanks.