The archive specified does not exist, MHonArc will automatically create the archive. If input is coming from standard in, then the input is treated as a single message to add to the archive. This can may cause the main index to be incorrect. When adding, MHonArc will skip any messages that already exists in the archive. This allows one to have MHonArc rescan a mail folder only add any new messages found.
NOTE MHonArc determines duplicate messages by message-ids.
The following shows how a single message can be added.