If your friend will also be running the DNS server for your domain, then copy down the DNS info from the Panel under Manage Domains section. By clicking "DNS" next to your domain name, it'll show your MX records and "mail.yourdomain.com" IP addresses.
I suggest you add something similar to this to your friend's DNS entries for your domain (double check the Panel for this info):
MX 0 fltr-in1.mail.dreamhost.com.
MX 0 fltr-in2.mail.dreamhost.com.
CNAME for "mail.yourdomain.com" as "MAILSERVER.mail.dreamhost.com"
You can get the mailserver name by clicking Account Status in the upper right corner of the panel.