The program  I used for  this comes with  LSMTP, it reads  the accounting
files (you need to enable full accounting). It could probably be modified
to work  with sendmail logs,  or perhaps one  could write a  program that
reads a  sendmail log  and outputs  a file  in the  same format  as LSMTP
accounting  records (I  can send  you the  specs). But  I know  that some
people  have written  similar utilities  that work  directly on  sendmail
logs. The metrics  may not be the same  but you will get an  idea of your
round trip times.
 
  Eric