NAME

       testmxlookup - Look up mail relays for a domain

SYNOPSIS

       testmxlookup [@ip-address] [--dnssec] [--udpsize n] {domain}

DESCRIPTION

       testmxlookup lists the names and IP addresses of mail relays that receive mail for the domain. This is
       useful in diagnosing mail delivery problems.

       testmxlookup sends a DNS MX query for the specified domain, followed by A/AAAA queries, if needed.
       testmxlookup lists the hostname and the IP address of every mail relay, and its MX priority.

   DIAGNOSTICS
       The error message "Hard error" indicates that the domain does not exist, or does not have any mail
       relays. The error message "Soft error" indicates a temporary error condition (usually a network failure
       of some sorts, or the local DNS server is down).

   OPTIONS
       @ip-address
           Specify the DNS server's IP address, where to send the DNS query to, overriding the default DNS
           server addresses read from /etc/resolv.conf.

           “ip-address” must be a literal, numeric, IP address.

       --dnssec
           Enable the DNSSEC extension. If the DNS server has DNSSEC enabled, and the specified domain's DNS
           records are signed, the list of IP addresses is suffixed by “(DNSSEC)”, indicating a signed response.

           This is a diagnostic option. Older DNS servers may respond with an error, to a DNSSEC query.

       --udpsize n
           Specify that n is the largest UDP packet size that the DNS server may send. This option is only valid
           together with “--dnssec”. If “--dnssec” always returns an error, try “--udpsize 512” (the default
           setting is 1280 bytes, which is adequate for Ethernet, but other kinds of networks may impose lower
           limits).

SEE ALSO

       courier(8)[1], RFC 1035[2].

AUTHOR

       Sam Varshavchik
           Author

NOTES

        1. courier(8)
           http://www.courier-mta.org/courier.html

        2. RFC 1035
           https://www.ietf.org/rfc/rfc1035.txt