Inside Macintosh: Open Transport /

Chapter 8 - TCP/IP Services / TCP/IP Services Reference

Functions / Getting Information About an Internet Host

OTInetMailExchange

Returns mail-exchange-host names and preference information for a domain name you specify.

C INTERFACE

OSStatus OTInetMailExchange (InetSvcRef ref,
                             char *name,
                             UInt16 *num,
                             InetMailExchange *mx);

C++ INTERFACE

OSStatus TInternetServices::MailExchange (char *name,
   UInt16 *num,
   InetMailExchange *mx);

PARAMETERS

ref

The internet services reference you obtained when you opened the TCP/IP service provider.

name

A pointer to a host name, partially qualified domain name, or fully qualified domain name for which you want mail exchange information.

num

A pointer to the number of elements in the array pointed to by the mx parameter. When the function completes, it sets the number pointed to by the num parameter to the actual number of elements filled in.

mx

A pointer to the first element in an array of InetMailExchange structures. You must allocate the structures in this array.

DESCRIPTION

In order to deliver mail, a mail application must determine the fully qualified domain name of the host to which the mail should be sent. That host might be the final destination of the mail, a mail server, or a router. The domain name system servers maintain mail-exchange resource records that pair domain names with the hosts that can accept mail for that domain. Each domain name can be paired with any number of host names; each record containing such a pair also contains a preference number. The mailer sends the mail to the host with the lowest preference number first and tries the others in turn until the mail is delivered or until the mailer decides that the mail is undeliverable.

The OTInetMailExchange function returns mail-exchange-host and preference information for the domain name you specify. You must then determine the address of the host and how best to deliver the mail. You can specify as many elements to the array of InetMailExchange structures as you wish.

If you call this function asynchronously, the TCP/IP service provider calls your notifier function with the T_DNRMAILEXCHANGECOMPLETE completion event code when the function completes. The cookie parameter to the notifier function contains the array pointer you specified in the mx parameter. If you had more than one simultaneous outstanding call to the OTInetMailExchange function, you can use this information to determine which call has completed execution.

SPECIAL CONSIDERATIONS

If you call this function asynchronously, do not write to the InetMailExchange array until the function completes.

COMPLETION EVENT CODES

T_DNRMAILEXCHANGECOMPLETE

0x10000004

The OTInetMailExchange function has completed.

SEE ALSO

The InetMailExchange structure is described in "Internet Mail Exchange Structure" on page 8-28.

Internet mail routing and mail-exchange resource records are described in Request for Comments 974: Mail Routing and the Domain System.