Actually, it doesn't. If you insert more than one rrow into the table that fires the trigger, the trigger will only process one row. You need to rewrite the code in a set based fashion to get all of the rows. Please see Books Online (press the {f1} key) and read up on the INSERTED and DELETED logical tables that are available when the trigger is doing its job.

It's also a pretty bad idea to call email in a trigger. If email is down, the trigger could fail which will rollback the external transaction. It's a far bettter thing to insert what you want into a staging table and have a job sweep through that tablee to send the emails.