There is no real obvious answer to decide whether an email from a trusted source is safe or not just from the address. The typical process being used by most businesses/people is to have their email server or an external source check every email for any one of the many problems.
Two examples are needed to describe the situation as it depends on your email system. First there are many quality products out there that will work with your email server to check each incoming and outgoing email for any possible issues. Second there are services on the Internet like Postini (no connection on my part) that you give permission to have your email re-directed through their servers and they check the email for the same issues.
There are many proponents to both approaches. It really just depends on your individual situation.