Showing results for 
Search instead for 
Did you mean: 

Delivery Failed Message

Posts: 23
Thanks: 3
Registered: ‎18-03-2018

Delivery Failed Message

Hi folks,

Not sure if this is the right place to ask this question so please bear with me and redirect if necessary.

Can any one you help please? We have been getting a ‘delivery failed message’ from one particular recipient. This has only started to happen in the last 2/3 days & we haven’t changed any settings. We can receive messages from this address. Sending/receiving from all other addresses is OK.

We have our own domain hosted by ionos and use plusnet for broadband.

The message we get is:

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of

its recipients. This is a permanent error.

The following address failed:


SMTP error from remote server for GREETING command, host: ( reason: 550 5.7.1 [C10] RBL restriction: Blacklisted by Internal Reputation Service -

I have checked

It says:

Our domain is not listed– all the lists have green ticks.

Our IP is listed on Spamhaus Zen.

We have also checked Spamhaus directly. It reports our domain is not listed and that our IP has 1 listing on its Policy Blocklist. The notes on the webpage say this should not affect sending or receiving e-mail.

We are using Thunderbird as our e-mail client set up using the details supplied by our domain host (ionos). It uses as the mail server.

Connection security = ssl/tls

Authentication = normal password


Regards Thackie

Aspiring Pro
Posts: 107
Thanks: 83
Fixes: 9
Registered: ‎08-07-2017

Re: Delivery Failed Message

That error looks like Centurylink are refusing an incoming connection from an SMTP server address they have chosen to blacklist - which is "" (I'd guess "mout" is probably "mail out")

Looks like you are using IONOS for your outgoing SMTP server, and "" is one of their servers according to

Similar error mentioned here as an example of another company being blocked by Centurylink.

(It would be normal for your PlusNet IP to be on a policy list, as typically an end user wouldn't do SMTP directly, they'd submit mail through the PlusNet smart relay, or in your case another company's relay.)

You'd probably best check with IONOS about this block and the reputation of their mail server.

Posts: 23
Thanks: 3
Registered: ‎18-03-2018

Re: Delivery Failed Message

Thanks for that.

I have contacted ionos to see what they can do.


Posts: 23,292
Thanks: 9,783
Fixes: 162
Registered: ‎22-08-2007

Re: Delivery Failed Message

This is not dissimilar to issues seen with other mail hosting services. The incorrect application of PBL rules seems widespread. There is a difference between email submission (as in an email client) and email relay as would happen if a user was running their own email server.

The PLB is intended to inhibit own hosted SMTP servers giving rise to spam mail. It should not inhibit email message submission from an email client.

This issue needs to be addressed to your hosting provider … do not accept “You need your ISP to sort this” as their “nothing to do with us” do nothing answer.

Superusers are not staff, but they do have a direct line of communication into the business in order to raise issues, concerns and feedback from the community.