What to do when your mail server is on a blacklist #
Sometimes an email does not arrive with one or a few of your contacts, because the IP address the mail was sent from at that moment is on a blacklist at the receiving provider. You recognise this by bounce messages with texts such as “blocked using” followed by the name of a blacklist. Worth knowing: our mail is sent through a large mail provider with a pool of rotating IP addresses. A block therefore applies to the IP address used at that moment; the next mail often goes out through a different address.
What is a blacklist #
A blacklist is a list of IP addresses that are temporarily or permanently blocked by mail providers because they have shown suspicious behaviour. This can happen to large mail providers because of the volume of email being sent.
Some DNS-based blacklists are not widely recognised or reliable. They can block entire IP ranges of large email providers, regardless of the reputation of individual senders. These blacklists often have no transparent criteria for listing, nor a fair process for getting removed.
Most large mail providers such as Gmail, Outlook and Yahoo do not use these blacklists for filtering, so the impact on your overall deliverability is usually minimal. Smaller or regional providers may use them, which can lead to blocking at a few recipients.
How to recognise a blacklist problem #
In the bounce message you see texts such as:
- “blocked using bl.cloud86-dnsbl.io”
- “Service unavailable; Client host blocked”
- “listed in blacklist”
The IP address mentioned is one of our mail servers, not your own IP address.
What you can do #
Step 1: reset the bounce status of the contact. Open the contact, set the status from Bounced back to Subscribed and send the mail again (or simply let the next mail in the series run). Because sending goes through rotating IP addresses, in many cases the mail then arrives without any trouble.
Step 2: check your own DNS settings. If it keeps going wrong with the same recipient, the cause usually lies not with the IP address but with the reputation of your sender domain. Receiving providers look at the SPF, DKIM and DMARC records of your domain; if something is missing there or an old record is still in place (for example from your previous mail system), that is the structural fix. How to check those records is explained in the guide on avoiding the spam folder. If you are not sure, email support with your domain name and we will go through the records with you.
Step 3: consider whether the recipient wants your mail at all. The recipient may have marked your email as spam earlier. So do not simply assume you can still mail this contact. If it is a customer you are certain wants to receive your mail, advise them to:
- Add your sender address as a safe sender in their email client
- Check whether the email may have ended up in the spam folder
If the problem persists after that, email support with the recipient’s email address and the full bounce text, and we will look into it.
What Autorespond does #
We monitor the sending reputation of the platform continuously. We deliberately do not request de-listing from a blacklist like that: the sending IP addresses rotate, so releasing one address has no lasting effect. What does help, we do together with you: resetting the bounce (step 1) and getting your DNS records in order (step 2). The latter is almost always the real solution, and it works for all recipients.
Preventing blacklistings #
To keep blacklistings to a minimum:
- Only mail contacts who have explicitly given permission
- Clean up inactive contacts regularly
- Always use a clear unsubscribe link in your emails
- Spread large mailings over several hours
- Follow best practices to avoid the spam folder
