The MX servers for a domain do not have to be in the same domain. Your SMTP servers should belong to one domain. List the outbound SMTP servers in the SPF record for the domains used in email addresses (usually rather than ). While it is common for the MX servers to also be the outbound mail servers, it is not necessary. (SPF can be used to verify the server as well as the sender.) This will allow recipients to verify that this server is intended to send mail. This will allow rDNS validation to work on the HELO or EHLO command.Ĭonsider adding an SPF record like v=spf1 a -all to the DNS entries for each SMTP server. Configure the mail server to use the service name as its identity.Configure your mail server to bind to the above address(es) when sending email.This will enable reverse DNS (rDNS) validation to work. Have you IP provider configure the PTR record to return the service (SMTP) name of the server.(You will need two PTR records if you are configuring both IPv4 and IPv6 support.) Also add an AAAA record for the mail server's IPv6 IP. Publish an A record in DNS for your mail server's IP address.Load balance your MX servers by publishing them at the same priority. For common services like SMTP, Web, IMAP, POP and other it is common to publish and use service names in addition (or instead of) host names. The domain you use for your mail server(s) rarely matches the server name. It is common to use names like for farms of servers. SMTP servers will be at the RCPT TO command, and may be attempting to deliver the same message to different domains for which you are listed as the MX. Incoming traffic will be part way through a conversation before you can route it appropriately.
If you don't get the configuration right, it is likely to hurt your ability to successfully deliver mail.
There is no need to put nginx or any other form of load balancer in front of your border SMTP servers.
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