1. First, have your contact email you FROM that address. Make sure that the email does not arrive in your Bulk or Junk email folder.
2. Reply to that email you received.
3. Have that person reply to your email.
These three steps do several things:
1. Validate that the sender is a valid email address.
2. Confirm that the Exchange server can "talk" to their email server.
3. Verify that your reply settings are set up correctly.
If you are unable to receive an email from your contact, it is possible their email server is having complications. If you are able to receive an email from your contact and not able to reply to them.
Three things may be causing this:
1. The recipients' inbound server/s may be having problems.
2. The outbound SMTP settings for your account, may be configured incorrectly.
3. The outbound SMTP server may be having complications.
