which part of a formal e-mail is optional?\nthe closing\nthe contact information\nthe persons last name\nthe…

Brief Explanations:

In a formal email, the closing (e.g., "Sincerely"), the person's last name (in the greeting if using a formal title like "Dear Mr. Smith"), and the salutation (e.g., "Dear [Name]") are standard and expected. However, contact information is often included but not always strictly required depending on the context and prior communication history.

Answer:

the contact information