No... not in ESA, its not that granular.
There are some external ways to add things you could block on, in no particular order
1. An ldap group (whether you did it in AD, or an ADAM instance or some other LDAP server)
2. 15.5 has API calls to do this now (edit the senders list in a policy), so a place that they could edit a list that got pushed into the ESA would work.
3. External Threat Feeds but you'll end up processing the mail more than you'd want to...
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