Moving to Sylpheed from PMMail

[stayler]

Well it seems the promised Linux version of PMMAil is pretty much a
piece of Vaporware so I'm looking to transfer some of my old PMMail
folders to Sylpheed.  PMMail uses directories and a somewhat strange
way of tagging msg's as individual files.  I understand that Sylpheed
is similar but the files are numbered in order.  Is there a simple way
in BASH to rename the files in a directory with numbers in ascending
order?  

stayler