If you are converting existing LDAP entries to calendar enabled entries, you must add the mail attribute to each user, group and resource LDAP entry that does not contain it.
To add the mail attribute to existing users, groups and resources, use one of the following methods:
Use Delegated Administrator Utility for a Schema version 2 Environment.
Use the commadmin user|resource|group modify -A option.
For example: commadmin group modify -A +mail:jdoe@sesta.com
Use the Calendar Server D.3 csattribute utility for a Schema version 1 environment.
The following example adds the LDAP mail attribute for an existing conference room named Room100 on the sesta.com server:
csattribute -a mail=Room100@sesta.com add Room100
Use ldapmodify to add the attribute directly to the LDAP entries for either Schema version.