General comments regarding email problems:

Starting
/usr/bin/maemo-summoner /usr/bin/modest.launch showui
may provide some output about the Email application itself (e.g. when it crashes).

If starting the Email application works and you "just" want to debug the connection to the mail server:

Start an X Terminal window and enter
export "CAMEL_DEBUG"="all"
to enable the debug mode of the mail library, and after that
/usr/bin/maemo-summoner /usr/bin/modest.launch showui > log 2>&1

to start the email application. Then try to connect to the mailserver. This will create a logfile named "log".

Please also make sure to run the latest version (4.2008.36-5). There have been a lot of Email related fixes since the release of 4.2008.23-14.