Put the exact text in DIR/prefix. You can include the message number assigned to the post in the list archive by adding the ‘#’ character in the text in DIR/prefix (example: put ‘lsqb;listname-#rsqb;’ in DIR/prefix). ezmlm does not modify the subject other than by prefixing it with the prefix. ezmlm knows about RFC2047 encoded subject and can detect a prefix within an encoded word. However, ezmlm will not modify the subject itself. It will add a prefix only of none has been added before. A consequence of this is that a message will have the message number prefix of the first message in the thread rather than a prefix with the number of the message itself. The entire thread can always be retrieved with a message to ‘list-thread-x@host’, where ‘x’ is the number in the prefix.
We recommend against using the prefix feature and strongly against the message number prefix. If you use it, make sure you understand the drawbacks, of message modification and subjects that change between message and reply. ezmlm can deal with this, but other programs may not be able to.
Sublists ignore DIR/prefix.
If you add a prefix, especially if you previously added it by other means (procmail, etc.), use ezmlm-idx to re-index the archive. Due to the way ezmlm-get(1) does threading from the subject, it works best if you use exactly the same prefix as you did before.