#SIMPLE DNS PLUS REVERSE IP NUMBER HOW TO#
You are responsible for activity on this IP address if you send email, so make it easy for people to know how to reach you. adsl.23. means that it is an IP address they are responsible for. Also remember, according to Best Practises, having a reverse DNS that appears to be part of your upstream provider is not good enough for an email server. You should also read some of the other Best Practises documents if you have this problem. The following bad example(s) will get rejected: The reverse DNS string sent should in the style of: In order to ensure that messages are not stopped by this check, make sure the HELO is a FQDN. It requires that the IP address of anyone trying to connect, have a reverse DNS entry for their IP Address. Although by ‘best practices’ the HELO ‘should’ be a fully qualified domain name that is publicly resolvable, this rule does not check for that as some operators may still be using a fully qualified domain name that is only used internally at their location. IF you DON’T have reverse DNS you probably have trouble sending to most places already. It is only on IP’s which have no authority that immediate 5xx denial is performed. NOTE! During temporary DNS outages, this normally will reject with a 4xx error, allowing for retries. Or they use these IP’s in dictionary attacks. Or they have hijacked devices and computers that have been forgotten about. Most Anti-Spam tools will reject email from places with no reverse DNS anyways, as this is a common trick of spammers to hide their identities. Normally ALL IP addresses should have a correct reverse DNS, and especially email servers. This rule performs simple checks on the IP Address that is attempting to connect. The principal is that ALL email servers have a correct entry in DNS that resolves, and it should resolve to the responsible party for the email server. Information for Email and Network OperatorsĪlthough email servers can by RFC accept connections from any IP Address most Best Practises documents insist that all identifiers are correctly used, and in the case of reverse DNS on the connecting IP Address this also applies. If you are a user sending email and it got blocked, you should read this section instead.If you are an email or network operator, you can continue reading this section.Normally, the reason you have reached this page is because a mail server has sent you a message when it rejected an email from you, or one of your users.
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