The following Microsoft article lists the attributes required for 'Mail-Enabled' objects.
Per Microsoft KB 275636 at:
The article lists the attributes required for creating 'Mail-Enabled' objects. Policies for 'Property Generation and Validation' can be used for validating the attributes for objects you wish to 'Mail-Enable'.
The mandatory attributes are:
- mailNickname: This attribute is the alias to the mailbox.
- displayName: This attribute is the text that is the readable name that represents you for mail delivery, and also in the address book.
- targetAddress: This attribute is the e-mail address to which you want to redirect the mail. This attribute is formatted like the proxyAddresses attribute, where there is a prefix that defines the address type, for example, "SMTP:email@example.com".
The optional attribues are:
- E-mail address attributes: If you specify one or all of these attributes, Exchange Server does not generate the defaults for you. If these attributes are not specified, Exchange Server generates all three attributes for you, based on the rules set up for your Exchange Server computer:
- proxyAddresses: A multi-valued attribute that contains all the e-mail addresses for which you can receive mail. The format of this attribute is PREFIX:proxy, where PREFIX is either SMTP, X400, GWISE, or NOTES, for example, SMTP:firstname.lastname@example.org.
- mail: This attribute contains the primary SMTP address for this mailbox. This attribute does not have an address prefix and it only contains the SMTP address, for example, email@example.com.
- textEncodedOrAddress: This attribute contains the primary x400 address for this mailbox. This attribute does not have an address prefix, and it only contains the x400 address, for example, c=us,a= ;p=First Organizati;o=Exchange;s=yip;g=geeman;.
- legacyExchangeDn: This attribute is a unique legacy distinguished name which identifies your mailbox. This attribute is mainly used for backwards compatibility purposes for MAPI clients, for example, /o=org/ou=site/cn=recipients/cn=gyip. If this attribute is not specified, Exchange Server generates a random distinguished name for you. This value contains the location of the physical object in the Exchange Server 5.5 directory service; therefore, if you specify a value here for the object in Active Directory, the ADC may change the value, depending on where the physical object is created by means of the ADC.