[BUG] Multihomed MX records use only a single IP

[AlexeyDemidov]

When we have multi-homed MX record(s) which resolves into multiple A records eg.

@ IN MX 0 mail.example.com.
mail.example.com. IN A 192.168.100.1
mail.example.com. IN A 192.168.100.2

Only a single IP address will be checked as Resolv.getaddress is used for MX hosts name resolution instead of Resolv.getaddresses.

[bestwebua]

Hi, Alexey! It make a sense, but what's wrong? In realization below we get array of mx records, and convert each mx record object to ip adress.

def mx_records(domain)
  Resolv::DNS.new.getresources(domain, Resolv::DNS::Resource::IN::MX).map do |mx_record|
    Resolv.getaddress(mx_record.exchange.to_s)
  end
end

[AlexeyDemidov]

Each MX record contains a single hostname but this hostname can have multiple A records so it resolves into multiple IP addresses. When a single hostname resolves into multiple IPs it is called multihomed host. In my example above you can see only one MX record but it resolves into multiple address. With this example current implementation using getaddress returns only one IP out of two (192.168.100.1 and 192.168.100.2) actually present in DNS for hostname mail.example.com. You need to use getaddresses to get an array of IP addresses returned for a single MX record.

[bestwebua]

Thanks for explanation, @AlexeyDemidov! I will fix it in next release 👍

[bestwebua]

Fixed!