.TH dns_mx 3
.SH NAME
dns_mx \- look up MX records for a FQDN
.SH SYNTAX
.B #include <dns.h>

void \fBdns_mx\fP(&\fIout\fR,&\fIfqdn\fR);
.br
void \fBdns_mx_packet\fP(&\fIout\fR,char *\fIbuf\fR,unsigned int \fIlen\fR);

stralloc \fIout\fR = {0};
.br
stralloc \fIfqdn\fR = {0};

.SH DESCRIPTION
.B dns_mx
looks up MX records for the fully-qualified domain name in \fIfqdn\fR. It puts
the MX records into \fIout\fR and returns 0.  Each MX record is a two-byte MX
distance followed by a \0-terminated dot-encoded domain name. If the
domain does not exist in DNS, or has no MX records, \fIout\fR will be empty.

If \fBdns_mx\fR has trouble with the DNS lookup or runs out of
memory, it returns -1, setting \fIerrno\fR appropriately. It may or may
not change \fIout\fR.

.B dns_mx_packet
is a low-level component of \fBdns_mx\fR, designed to support
asynchronous DNS lookups. It reads a DNS packet of length \fIlen\fR from \fIbuf\fR,
extracts the MX records from the answer section of the packet, puts the
results into \fIout\fR, and returns 0 or -1 the same way as \fIdns_mx\fR.

.SH "SEE ALSO"
dns_ip4_qualify(3), dns_ip6_qualify(3), dns_name4(3)