You should apply the following five tests to every piece of e-mail, with an attachment, that you receive.
If any test fails, toss that e-mail out. If they all pass, then you still need to watch for unexpected/suspicious results when you read/open the email attachment.

1. The Know test: Is the e-mail from someone that you know?

2. The Received test: Have you received e-mail from this sender before?

3. The Expect test: Were you expecting e-mail with an attachment from this sender?

4. The Sense test: Does the e-mail from the sender, with the contents described in the Subject line, and the name of attachment's make sense?

5. The Virus test: Does the e-mail contain a virus? To determine this, you need to install, maintain, and use an anti-virus program at all times.