Update on the above.
Upgraded to the latest svn tarball version from sourceforge (nightly 20070612). This has a preview pane and html mail composition. But the html mail compose seems to be slightly buggy.
Something very strange is happening. A user is able to delete the default identity from the identities tab, even if there is only one identitity defined. Once this is done, the sender identitity is lost from the sender pull down. Mail cannot be sent from the users ID anymore.
On looking up the database, it is seen that the identitities table shows the deleted idenitity as DEL=1. If this is restored to DEL=0, sending operation becomes successful.
If more than one identitity is defined, user can send mail from the other identitity.
This seems to be a real bug. It seems to be logical to incorporate a script which would delete the user from the users table also, if his lone default identitity in the base domain is deleted. Or it would be still more logical to prevent users from deleting their lone identitities in their base domains. They may set this to non-default if they so desire, but no deletion.
Hope the develpment team will look into this.
I removed the identitities tab from the preferences to prevent a recurrence.
kmn