The EmailRuleSetService component, configured in CommerceAccelerator/Applications/B2CStore/Plugins/Checkout/src/main/config/atg/targeting, defines the rule that states a customer must have an email address associated with her profile in order to view the checkout page. It should be configured as follows:

$class=atg.targeting.RuleSetService
$description=Defines rule set for access controller.

# The rule.
ruleSet=<ruleset>\n  <accepts>\n  <rule op\=and tag\="Show">\n  <rule op\=and
tag\="Content">\n  </rule>\n  <rule op\=and tag\="Environment">\n  <rule
op\=neq>\n  <valueof target\="email">\n  <valueof constant\="null">\n  </rule>\n
</rule>\n  </rule>\n  </accepts>\n</ruleset>

# Should we check whether the rules file has changed.
updatesEnabled=true

# Time interval after which to check whether the rules file has
# changed; if 0, the check will be performed on each request.
rulesFileCheckSeconds=0