The MIME standard (RFC 2046) provides the message/partial content type for breaking up messages into smaller parts. This is useful when messages have to traverse networks with size limits. Information is included in each part so that the message can be automatically reassembled once it arrives at its destination.

The defragment channel keyword and the defragmentation channel provide the means to reassemble messages in PMDF. When a channel is marked defragment any message/partial messages queued to the channel will be placed in the defragmentation channel queue instead. The defragmentation channel maintains a database which is used to match the parts of each message up with each other. Once all the parts have arrived the message is rebuilt and sent on its way.

All channels that perform local delivery or send messages on to networks that cannot deal with fragmented messages should be marked with the defragment channel keyword. The defragment channel keyword will have no effect unless a defragmentation channel is also defined.

A defragmentation channel is produced automatically by the PMDF configuration generator.