[Exim] host_reject_recipients question

I'm pretty sure of it's behavior, however I would like confirmation.
Does host_reject_recipients do a DNS lookup, or just a match of text?
I appears to be doing a DNS query, and any hosts, IP or FQDN, it can't
resolve, it rejects.
Is this correct?

Owen C. Creger CCNA
Information Systems Security Engineer
Creative Solutions Inc.
7322 Newman Blvd.
Dexter, MI 48130
email: ocreger@???
ph: 734-426-5860 ex. 3787
fax: 734-426-5946
cell: 734-223-6270