Remote host address is the local host is an Exim error message which indicates that the sender or recipient's domain has your machine's hostname/IP, but Exim is not configured to accept mail for that domain.

Exim has a standard domainlist named +local_domains that pretty much every different Exim configuration system uses. See what domains are configured for your system by running:
exim -bP '+local_domains'

You will probably see a command that looks up a list of domains from a file. Put your hostname in that file and Exim should begin to work properly.