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