Try these questions to test your knowledge from this chapter:
- What port does SMTP operate on?
 - How do you determine which SMTP server receives mail for a given domain?
 - How do you determine which SMTP server sends mail for a given provider?
 - Why won't an SMTP server relay mail without authentication?
 - How are binary files sent as email attachments when SMTP is a text-based protocol?
 
The answers can be found in Appendix A, Answers to Questions.