Name resolution is the process of determining a
machine's IP address based on its fully qualified
domain name. This is done by using the Domain Name System (DNS). The
process that sendmail uses to resolve a name is
described in Section 9.2.
When sendmail finds that a hostname is really an
MX record, it attempts to look up the address (which can be an A or
AAAA record) for the host that handles mail receipt. That request can
fail for a variety of reasons. If the -d8.1
(a.k.a. -d8) debugging switch is specified,
sendmail produces the following message:
getmxrr: res_search(host) failed (errno=errornum, h_errno=herrornum)
Here, host is the hostname that was looked up,
errornum is the system error number (if any)
from <errno.h>, and
herrornum is the resolver-specific error number
from <netdb.h>, as shown in Table 16-7.
Table 16-7. Resolver errors from <netdb.h>
|
-1
|
NETDB_INTERNAL
|
Error in the lookup code, see errno=
|
|
0
|
NETDB_SUCCESS
|
Success
|
|
1
|
HOST_NOT_FOUND
|
Host not found
|
|
2
|
TRY_AGAIN
|
Temporary DNS server failure
|
|
3
|
NO_RECOVERY
|
Nonrecoverable errors and refusals
|
|
4
|
NO_DATA
|
Valid name but no record of requested type
|
