Email Bouncing / RBLs

Article ID: 83

Why is email that I am sending to an Infinity Internet user being rejected?

Someone is trying to send me email but it is being rejected. Why?

Have you been having troubles receiving email from someone recently? Do they get a message back to them stating that mail has been rejected? Are emails you are sending to an Infinity Internet customer being rejected and bouncing back to you? There are two reasons this could be happening, sender's ISP's (Internet Service Provider) mail server is on a Realtime Blackhole List (RBL) or has invalid rDNS records.

In an effort to combat spam we have recently made several changes to our spam filtering service. One change is checking for a reverse DNS or rDNS entry for all incoming mail.

Reverse DNS, or rDNS, is the process of finding the mail servers host name from it’s IP, this is found by checking a record held by the ISP which controls the IP in question. Any mail sent to our mail servers, will require valid rDNS or the sending mail server will be added to a blacklist.

Most ISP’s have valid rDNS records already set up for their mail servers. However this could necessitate some changes for those who run their own mail servers.

If you are running your own mail server and have issues sending mail to addresses handled by us, or you already know you do not have a rDNS entry set up, you will need to contact your ISP (This would be us, If you get your internet connection from us) and request that a rDNS record be added. This record would need to include your mail servers IP address, and the host name associated with it.

RBL lists

Created by Mail Abuse Prevention System (MAPS) LLC., Realtime Blackhole List consists of IP addresses whose owners refuse to stop the proliferation of spam.

The RBL usually lists server IP addresses from ISPs whose customers are responsible for the spam and from ISPs whose servers are hijacked for spam relay.

As subscribers to the RBL, ISPs and companies will know from which IP addresses to block traffic. Most traffic blocking occurs during the SMTP connection phase. The receiving end will check the RBL for the connecting IP address. If the IP address matches one on the list, then the connection gets dropped before accepting any email from the spammer. Some ISPs, though, will choose to blackhole (or ignore) IP addresses at their routers. The goal here is to block all IP traffic.

Those offenders who wish to be removed from the list must drop the spammer, strengthen their Acceptable Use Policy (AUP), and often, tighten the security settings on their mail servers to prevent future occurrences.

Let's go over what to look at to diagnose the problem. If you are the one who cannot receive email, ask the sender to carefully read you the error message that was returned to them. If you are the sender, have a copy of the error message on hand. Often this will tell us what the exact problem is.

The most common "bounce-back" error messages will look like one of the following examples:

This Message was undeliverable due to the following reason:

The following recipient was rejected by a remote mail server.
The reasons given by the server are included to help you determine why each recipient was rejected.

Recipient: <


----- The following addresses had permanent fatal errors -----
<> (reason: 550 Service unavailable; Client host [] blocked using; Blocked - see

Now let's decode these errors:

Recipient: Address the email was sent to
[] blocked The number inside the brackets [ ], is the IP address of the mail server that the email was being sent from (the sender's ISP) and is the address of the server that is being blocked.

You can copy and paste the IP address into this website to see if it is on more than one RBL:
(address may vary)
The website address of the Realtime Blackhole List
<> A direct link to the RBL's website with detailed information as to why this particular server is on the blackhole list.

Search the RBL lists now:
Now that you know what that error message means, let's search for the IP Address from the error you received. If it is not already filled in for you, type in the IP Address in the box below and click the GO! button:

Why is this person/ISP on an RBL?:
When a Spammer sends out mass email, it generally goes out to a large amount of people. Some of these people look at the message and see where it comes from and then forward the offending message to that person's ISP. At this point, the ISP can either deal with their user or choose to ignore the issue. Some ISP’s are SPAM friendly and take no action. Some people and/or ISP’s choose to forward these Spammers to the RBL’s to have them looked into. If the RBL’s find that it is genuine, they will add the IP address to their servers, and others that subscribe to those services will no longer accept mail from that IP address, and return a message similar to the above.

Now that you know what the problem is and have detailed information about it, the next step is to have the sender email their ISP's technical support department with a copy of the information found from your search. They will be able to look at the information that has been provided and take the necessary steps to remove their server from the RBL (and probably appreciate the research you have done for them!)

We understand that the RBL can sometimes cause some inconvenience, but by using it, we are dramatically reducing the number of spam emails that you receive.

Is there some way I can get around the RBL and get mail from these people?:
There is no way for you to be able to get an IP address off of an RBL yourself. This would be akin to someone calling your bank and being allowed to change your account information without any sort of confirmation. We do offer one way to bypass our filters for your account. This will allow you to receive email even from people who are listed on RBL lists, however, it will also allow all mail to be delivered to you. We strongly advise against this, as the amount of junk email (SPAM) being delivered to your mailbox will increase a great deal. If you still wish to have this done, please contact us via Live Support Chat, email, or by phone.

If you need further assistance regarding this issue, contact our technical support department by emailing