Every messaging user is associated with an address type, a character string describing the format of the user's address that is stored in the PR_ADDRTYPE property. Address types map to address formats. That is, by looking at a recipient's address type, client applications can determine how to format an address appropriate for the recipient. For example, the address type MS describes an address with three components separated by slashes as indicated by the following entry:
network/postoffice/mailbox
Likewise, the SMTP address type describes the standard Internet address:
username@companyname.com.
All address book entries must have a valid address type. Clients require their users to specify an address type when creating a type of custom recipient unsupported by the address book provider. For the entries that they support, address book providers are required to supply valid address types.
MAPI defines only one address type: MAPIPDL, which stands for personal distribution list. Microsoft publishes address type definitions for those messaging systems that it makes, such as MS. Other definitions are taken from the vendor or standards body that owns them. The complete list of address types is included in an appendix, Address Types.
To get a list of the address types supported by all of the transport providers in the session, clients call the IMAPISession::EnumAdrTypes method.