Blocked at

On Tuesday, June 9th, 2020, various mail server administrators were reporting that they were now having trouble delivering email messages to large German ISP and mailbox provider (and telecommunications company) T-Online.

In various tests, many people who connect to port 25 of any of the  inbound mail servers for the domain are immediately greeted with this error message: 554 IP=[YOUR IP ADDRESS] - A problem occurred. (Ask your postmaster for help or to contact to clarify.) (BL)

As the error messages contains (BL) which suggests spam blocking, but it is being reported by multiple, unrelated entities, who are not sending spam or perhaps are not sending much mail at all. I and others were wondering, could be a spam filter be incorrectly configured?

I reached out to T-Online to request clarification. They explained: "In principle, our system does not accept e-mail from hosts with bad or unknown reputation. Hosts with unknown reputation may include such hosts that have not send e-mail for a very long time (longer than at least a year)."

In other words, they're saying that they block unknown IP addresses automatically until you reach out to them to request that email messages from your IP address be allowed through. That seems a bit harsh to me, and against the principle of innocent until proven guilty, but such is life.

If you've been affected by this issue, feel free to let me know in the comments below.


  1. Unfortunately, it is not enough to contact them to get your ip-address unblocked. Not that I haven’t tried this! They require that you to build a web-page that contains all your address information. A plethora of joy for all spammers, telephone marketeers, identity thieves and other black-hats!

  2. "They require that you to build a web-page that contains all your address information. "
    is there a link to such a form?

  3. We have the same problem sending mails to their users.
    Because this behavior comes from a decision made by t-online, we decided to stick with our SMTP/SPF/DKIM configuration as it is (and not causing any trouble). If a user from t-online complains, we kindly tell them to speak to their provider.

  4. This comment has been removed by a blog administrator.

  5. A poor German student wrote me to have an Internship with our company and I can't answer her because of this issue. I think this is a colossal mess-up from Deutsche Telecom and they still didn't realise the issue. Time of a week, couple of people fired and then it will be back to normal.


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