Sent emails are 'returning'? What now? | AltusHost

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Sent emails are ‘returning’? What now?

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Even though a blacklisted IP address can be troubling for your business, it seems that there is not enough buzz around that talks about ways to prevent it.

But what exactly does this mean for your website?

Besides the obvious damage in your server’s reputation, a blacklisted IP address can also cause blacklisting of the main IP address in the entire Shared Hosting server. 

And to put this mildly, it’s simply not good. 

You are not alone in the Shared Hosting server, remember? This server is “shared” with a couple of hundred other users, whose emails may be directly compromised by your blacklisted IP address. 

How to prevent a blacklisted IP 

Let’s go into a mini-analysis first…

In many cases, if your email address is blacklisted, the first thing you will notice is that the emails you send are coming back.

What’s the backend of this? In the case of a low reputation of the outgoing server, all outgoing mail is rejected by the receiving server, and in the case of blacklisting – because the server is on one of the “blacklists” of one or more RBL services.

RBL stands for Real-Time Black List and is a set of global IP addresses of ‘those who refused to stop spamming’.

RBL lists are most commonly used in the SMTP (Simple Mail Transfer Protocol) connection phase when your email server starts the login process to send emails to recipients.

The receiving SMTP server then checks if the transmitting server’s IP address in on one of the selected RBL lists.

If the transmitting server is blacklisted, communication is shut down even before the transmission of the e-mail starts.

But don’t panic, anyone with an SMTP server happens to be on one of the RBL lists.

In that case, it is necessary to find the cause of blacklisting, debug and retest the system. 

Resolving these issues can be fairly tricky, primarily because RBL services typically respond to IP addresses remove requests on an average of 24-48 hours after the submitted request. 

So, even after the technical support team fixes the reason the server was blacklisted in the first place, it takes a couple of days for the RBL service to respond and remove the IP address from the list.

The bad news is that while the server is blacklisted, your emails will go to the recipient’s SPAM folder. In some cases, the mail does not even reach the final recipient.

Also, depending on the hosting provider, an outgoing check is also done, i.e. proactive check of the recipient.

In that case, the IP addresses of your recipients are also checked for blacklisting, and if they are on the blacklist, you guessed it – the mail will not be delivered.

For this reason, we advise our users to keep an eye on the status of their IP address, so that similar situations exist only in theory.

transmitting server

How to check the status of your public IP address?

Copy your IP address and check the status at:

My address is blacklisted! Now what?

In case your public IP address is blacklisted, do not panic.

Contact your provider as soon as possible and ask technical support to assign you a new IP address or try to remove your existing IP address from the blacklist.

The safest method is to lease a dedicated IP address.

Also, check the contact forms on your site and secure them.

I am not a robot

It would be good to put some kind of security check on pages that require user interaction, in order to prevent massive inbox spamming.

CAPTCHA has proven to be the most effective method of spam prevention. This system of “I am not a robot” was created at Carnegie Mellon University in 2000. The acronym CAPTCHA is based on the word capture and is derived from the term Complete Automated Public Turing test to tell Computers and Humans Apart.

The idea behind the system is to create an automatically generated challenge, that it is easy for humans, and unmanageable for computers and software. The most common CAPTCHA consists of an image with distorted letters, with different colors, colorful backgrounds, or other elements that make it impossible for the software to solve the test.


This technology seems geeky and boring, but believe it or not, every time you type in letters and numbers as required by the reCAPTCHA system you help in digitization of books and other publications. Specifically, reCAPTCHA does not display random words, numbers, and punctuation, but rather content from The New York Times archive and numerous books from the Google Books project.

Sites using the reCAPTCHA system show images of scanned words that optical character recognition software could not read during the process of digitizing books and magazines. The idea is very simple but effective, and very cleverly implemented, as it relies on the global “workforce” of all Internet users.

But CAPTCHA systems, of course, are not perfect. Apart from them annoying users, they are constantly under attack.

Because of this, CAPTCHA is just one small aspect of protecting your site from spam attacks.

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