In OSX Finder, go to Utilities and launch Directory Utility. Under OSX 10.6 Snow Leopard, Directory Utility is tucked away in /System/Library/CoreServices.

Choose Show Advanced Settings, switch to Services tab, select LDAPv3 and click the pencil icon (you may need to unlock settings with your admin password first):

Click New...:

Enter DavMail server name (localhost) and click Manual:

Enter Configuration Name and choose OpenDirectory in LDAP Mappings:

Enter o=od as Search Base Suffix:

If DavMail LDAP listen port is not 389, edit the new configuration, check Use custom port and enter actual port:

Then activate authentication under the Security tab and enter your credentials:

Under the Search Policy tab, choose Contacts, set Search to Custom Path and /LDAPV3/localhost to the list of Directory Domains:

Proceed to OSX IMAP Mail setup