Christian, thanks for the responses, but they’re too cryptic for me:
I knew to set columns as described; the question is how to set the defaults? Yesterday, for example, I had the columns the way I wanted them. Today, when I opened the same database, the columns had reverted to something inappropriate for an email archive. Other times, the columns I specify seem to stick (for awhile). Is there something subtle about saving the default column settings for a given database, given that I use multiple databases, which are often open simultaneously? Only one data base is for mail (for which I need From and To columns); the others are more normal and I want things like Name.
I could not interpret your answer to searching, e.g., for a data range). You refer to “predicates of smart groups” or "search for ‘Meta Data’ " I don’t know what the meta data is for Entourage and Mail messages stored in DT, but is seems not to include date information (DT manual item for Meta Data). And, if it does, I don’t know how to enter the date so that DT would recognize that I was looking for items before or after the entry. I also created a smart group to experiment with finding, e.g., messages in a date range. So far as I could tell, I could only specify fairly trivial things like “yesterday,” as distinct from “between 2000 and 2002”.
I believe that DT is limited by Snow Leopard, which in turn has worse search capability in some respects than earlier (or so it seems).
There are no defaults, the settings are remembered for different views/windows/databases. E.g. if you’re always using the same view (e.g. 3-pane view) and only one database, then the columns should be specific for each window.
Searching for date ranges isn’t possible yet and smart groups support only few ranges now (today, yesterday, this week, last week etc.).
The “Meta Data” option of the Search window or the toolbar search should find emails from a certain author but probably additional documents too. To have a look at the meta data of email, just select an email, open the Info panel and expand the “Additional Information”.
DEVONthink is using its own search engine but some more options (like searching for date ranges) are not yet available but will come.