All the search on the database is made with boolean phrases, you can use parentheses and logical operators (and, or) as you want. To search for complete phrases you can use "". In case you don't follow these rules some changes (watch the examples below) on your string will be done.
Use Find on the main page if you want to search only in the messages bodies.
Examples:
Search string separated with spaces:
will be converted to:my house
my and house
so, if you really want to search my house you should try:
"my house"
Using parentheses:
will be converted to:("my house")car
(my house) and car
so, if you want to search (my house) or car you should try:
("my house") or car