This patches exim to split the spool directory to 62x62 directories instead of just 62. It is for improving performance on systems with large exim queue.

    Q: How is this improving performance?

    A: High mail traffic servers are configured to queue the messages if load average is above a certain number ( usualy 4-10). If the traffic is really high then the queue will increase from thousands to millions of messages. if all messages were kept in one single directory then it will be really hard for the operating system to open that directory and write a new file there or to read a file from that directory. A good idea was to split that directory ( the spool ) into subdirectories ( 62 ), but on large queues the subdirectories are still hard to access. So this patch splits the spool directory into 62x62=3844 directories thus each directory will be easier to access because it contains less files. This improves both the queue runner ( part of exim program that scans the spool dir for detecting messages that need to be sent ) and the part that queues a message.