Can I Make the Email Address Optional?

Not in a Competition. Every Competition asks entrants for their name and email address, and you can't switch that off.

You do have two other options:

• In a Rewards campaign, turn off Capture User Details under User Details on the Pre-Entry tab, and people can claim without giving an email. See Rewards User Details.
• Any extra field you add under Add Custom Fields, such as a phone number or address, has a Required checkbox. Untick it and entrants can skip that field. Custom fields are on the Business Plan & above.

Every required field is one more reason for someone to give up before they enter, so only ask for what you'll actually use. Field types and settings are in Custom Fields.