What to do when your IP address is on a blocklist or your mail is rejected?

Updated: 28 September 2026 · Applies to: Email sent from your own server

Your mail is refused with a message about reputation or a blocklist, or a checker shows your IP address on a list. This guide gives the steps that work: find out why, stop the cause, and ask for removal. It also explains why moving the same mail to another address does not help.

1. Confirm the problem

1. Read the bounce or deferral text (How to read Postfix logs and understand common SMTP error codes?). It often names the list and gives a link.
2. Look up the address on the list's own website (for example the Spamhaus checker) and read the reason and the removal rules.
3. Note which provider refuses you. A refusal by one provider is not necessarily a public blocklist; it can be that provider's own reputation system.

2. Pause the affected sending

Stop the mail that leaves from that address until you know the cause. In Postfix you can put the queue on hold: sudo postsuper -h ALL (release later with sudo postsuper -H ALL) or stop the sending programs. Keep the other addresses running only if the problem is clearly limited to one stream.

3. Find the cause

• A compromised account or script. Look for unexpected mail in the queue and log: postqueue -p | head -50, and for sending programs that you did not expect (How to protect your mail-sending server from misuse?).
• A list with bad addresses or without consent. Many bounces, complaints, or recipients who do not know you (How to process bounces and spam complaints and keep a suppression list?).
• Missing authentication or reverse DNS. Check SPF, DKIM, DMARC and PTR (Gmail, Yahoo and Microsoft requirements for bulk senders: a checklist, audit commands).
• A sudden jump in volume. Compare today's numbers with the days before (How to warm up a new sending IP address step by step?).
• Website forms used to send spam through your server (contact forms without protection).
• The address had a past history. If the address was already listed when you got it, tell support at once (How to check whether a new IP address is on a blocklist before you use it?).

4. Fix it, then ask for removal

1. Close the hole: remove the compromised program, change passwords, clean the list, add the missing DNS records, and put limits in place.
2. Follow the removal process of the list you are on. Most lists want a short description of what you changed, and some remove the entry automatically after some time when the problem is gone.
3. Do not ask for removal again and again without changes; that slows the process.
4. After removal, restart carefully with a low volume and grow again (How to warm up a new sending IP address step by step?).

Why moving to another address is not a solution

• The cause travels with the mail. The same content, list and habits get the new address into the same trouble.
• A new address has no reputation at all, and providers often treat unknown addresses more strictly than an address with a good history.
• Some lists judge the whole network block, so a listing can cover the neighbouring addresses too.
• Ucartz's terms do not allow swapping the addresses of a delivered server on request, and the Acceptable Use Policy does not allow moving a stream to other addresses to keep sending after a block or complaints instead of fixing the cause.

Working with Ucartz support

Open a ticket with the address, the list or provider, the error text and the date. The Acceptable Use Policy says that Ucartz may pause or restrict sending for high bounces, complaints or abuse reports, and that clean-up or delisting work for blocklisting caused by your use may be billed. Our engineers can also help you find the cause on your server, by the task.

Frequently asked questions

How long does removal take?
It depends on the list: some remove entries within a day after the problem is fixed, others need days or weeks.

Can I prevent listings?
Yes, mostly: consent, clean lists, authentication, warm-up, low complaint rates and monitoring (How to monitor your sending IP addresses automatically with a script?).

Need a dedicated server, more IP addresses, or a hand with the setup?

• Unmanaged dedicated servers: full root access and IPv4 subnets from /29 up to /24, ordered with the server or added later.
• Managed dedicated servers: our team looks after the operating system, updates, security and monitoring.
• Dedicated server locations: choose the country and data centre when you order.

Prefer a hand with the setup? Our engineers can do it for you: Hire an Expert, or use our on-demand server management.