Domain Sending Spam or Emails Blacklisted? What It Means and What to Check
If you are told your domain is sending spam, or your emails are being blocked or blacklisted, one of two things is happening. Either someone outside your business is forging your address on spam they send from their own systems, or something you own (a mailbox, your website or a contact form) has been compromised or abused and really is sending the spam. The two need different fixes, so the first job is to work out which one you have.
Forgery is a nuisance that email authentication settings deal with. A real compromise is a security incident that needs someone technical, usually whoever provides your website and web application development, along with your email or hosting provider.
What does it mean when my domain is sending spam or my emails are blocked?
It means receiving mail servers have seen spam carrying your domain name, or coming from the server your email uses, and now distrust it. You see that as messages landing in spam folders, bounces that say "blocked" or "rejected", or a warning from your host.
Situation 1: someone is forging your address
Email lets a sender type any address into the From line. Spammers use real domains because they look trustworthy. Nothing of yours has been broken into. Three DNS-based settings exist to counter this: SPF and DKIM let you declare which servers may send for your domain, and DMARC, defined in RFC 7489, lets you ask receivers to take no action on, quarantine or reject mail that fails those checks, and to send you reports.
Situation 2: your own mailbox or website is sending it
Here the spam genuinely leaves your account or server. Typical causes are a stolen mailbox password, a hacked website sending mail in the background, or a contact or signup form that bots are using to push messages out through your server. This spam can pass authentication checks, because it really does come from you.
How do I tell whether my address is being forged or my own system is compromised?
Look at where the evidence comes from. Evidence only from strangers points to forgery; evidence from inside your own accounts points to compromise.
Signs of forgery: you receive bounce messages ("Undeliverable", "Mail delivery failed") for emails nobody at your company wrote, those emails are missing from every Sent folder, and your normal email still arrives fine.
Signs of compromise: your host emails you about outgoing spam or suspends outgoing mail, your email provider restricts a mailbox, the Sent folder contains messages the owner did not write, replies arrive to emails nobody sent, or your contact form inbox fills with junk submissions. Microsoft, for example, blocks a Microsoft 365 user from sending when limits are exceeded and describes that as an indicator of a compromised account.
What is an email blocklist and how do I get removed from one?
A blocklist (often called a blacklist) is a published list of IP addresses or domain names that an organization has seen involved in spam; mail servers that subscribe to the list use it to reject or filter mail. There are many lists, each run independently, with its own lookup page and its own removal process. No single form clears you everywhere.
Spamhaus runs some of the most widely used lists. Its Domain Blocklist page explains that legitimate domains get listed when they are abused, often after a compromise of website software such as a CMS, that most listings expire once the activity stops, and that there is never a fee for removal. Its FAQ says listings are checked with the Spamhaus Checker and that removal requests must come from the registered owner of the domain or IP; otherwise you ask your service provider. On shared hosting the listed IP usually belongs to the host.
Large mailbox providers also keep private reputation scores. Google Postmaster Tools shows how Gmail sees you, with dashboards for spam rate, IP reputation, domain reputation and authentication, covering mail sent to personal Gmail accounts only.
What can I safely check in about 10 minutes?
Everything below is looking, not changing. Take screenshots as you go.
- Open one bounce or block message and read it fully. Note the date, the recipient, the error text, and any blocklist name or IP address it mentions.
- Ask the affected staff to check their Sent and Outbox folders for messages they did not write.
- Search your inbox and spam folder for messages from your hosting company and your email provider containing "abuse", "spam", "suspended" or "limit".
- Sign in to your hosting control panel and your email admin console and look for warning banners, suspended outgoing mail, or restricted users.
- Look at your contact form inbox. Hundreds of nonsense submissions in a short period means bots are abusing the form.
- If a block message names a blocklist, go to that list's own website and enter your domain in its lookup tool. Read the result; do not request removal yet.
- If Google Postmaster Tools is already set up for your domain, open it and note the spam rate and reputation readings.
If a Sent folder shows messages the owner did not write, have that person change the mailbox password and turn on two-step verification. Be aware of one side effect: if your website sends its contact form or order emails through that same mailbox, those emails stop sending until a developer updates the password stored in the website, so tell your developer as soon as the password is changed.
What should I not do?
- Do not request blocklist removal before the cause is fixed. The spam continues and you get listed again.
- Do not pay anyone for delisting. Spamhaus states that there is never a charge or fee for removal from its lists.
- Do not edit DNS records, including SPF, DKIM or DMARC, yourself. One wrong character can stop all your legitimate email.
- Do not delete suspicious files, emails or form entries. They are the evidence a developer needs.
- Do not keep re-sending blocked messages or switch to a mass mailing from a personal account.
When should I call a developer, and what should I have ready?
Call a developer as soon as there is any sign of compromise: a host warning, restricted sending, unfamiliar Sent items, an abused form, or a blocklist listing. Setting up or tightening SPF, DKIM and DMARC for a forgery problem is also developer work, because it means DNS changes.
- Two or three complete bounce or block messages, forwarded as attachments so the hidden headers survive.
- The exact text and date of any warning from your host or email provider.
- Screenshots of blocklist lookups and Postmaster Tools readings.
- The date the trouble started and anything that changed shortly before: new plugin, new form, new staff, a newsletter send.
- Who provides your domain, DNS, hosting and email, who holds each login, and every system that sends email as your domain (website, CRM, newsletter tool).
How do I stop it happening again?
Close the route the spam used, then make your domain harder to imitate. Ask your developer to set up SPF, DKIM and DMARC for every service that sends as your domain. As of October 6, 2026, Google's email sender guidelines require SPF or DKIM from all senders to Gmail, all three from anyone sending 5,000 or more messages a day, and a spam rate in Postmaster Tools below 0.3%.
On your own side: two-step verification on every mailbox, website software and plugins kept updated, bot protection and rate limits on every public form, and someone assigned to read Postmaster Tools and DMARC reports. Our web application security checklist for business covers the wider set of controls.
Quick answers
Does a bounce message for an email I never sent mean I was hacked?
Not necessarily. If the message is not in any Sent folder and your normal email still works, a spammer most likely forged your address on mail sent from their own systems. If the message is in a Sent folder, treat the mailbox as compromised.
What is an email blocklist?
An email blocklist, also called a blacklist, is a published list of IP addresses or domain names seen sending spam. Mail servers that use the list reject or filter mail from anything on it. Each list is run separately and has its own lookup and removal process.
Does it cost money to get removed from the Spamhaus blocklist?
No. Spamhaus states there is never a charge or fee for removing a listing, so treat any request for payment with suspicion. Removal must be requested by the registered owner of the domain or IP address, or by the service provider.
Will SPF, DKIM and DMARC stop my domain sending spam?
They help against forgery, where outsiders fake your address, by letting receiving servers reject mail that did not come from your approved senders. They do not help when your own mailbox or website is compromised, because that spam comes from an approved sender.
Can a website contact form cause my domain to be blacklisted?
Yes. Bots can submit a form thousands of times, and if the form sends a copy or confirmation to an address the bot supplies, your server ends up emailing strangers. Receivers then treat your domain or server IP as a spam source.
Conclusion
A domain "sending spam" is either being imitated or being used. Bounces for mail you never sent, with clean Sent folders, point to forgery. Host warnings, strange Sent items or a flooded contact form point to a compromise that must be closed before any blocklist removal is worth requesting.
Entrant Technologies builds websites, web applications, mobile apps and custom software. If you have no developer available, contact us and we will take a look.