Email Blocked: Why Your Message Was Blocked and How to Fix It

A message that says your email was blocked, rejected or refused is frustrating, and the text is often cryptic. The cause might be a typo, a security setting at the recipient's company, a failed authentication check or a problem with your sending reputation. This guide helps you work out why an email was blocked, what the common messages and codes mean, how to fix the problem whether you are an ordinary sender or run a business that sends email in volume, and what to do if the block is on the receiving side.

What does "email blocked" mean?

A block happens when a server refuses to accept a message, or when a security tool stops it before it reaches the mailbox. Two broad cases exist.

• Rejected during delivery. The receiving server answers your sending server with a permanent failure, a 5xx code, and your server sends you a bounce. You see this as an error message, often from Mail Delivery Subsystem. See what Mail Delivery Subsystem means.
• Accepted, then quarantined or discarded. The server says yes, and then a filter holds the message in quarantine or drops it. The sender may see no error at all. Only the recipient's administrator can find it.

Knowing which case you are in tells you who can help. A bounce gives you a reason. A silent drop needs a conversation with the recipient.

Common reasons an email is blocked

1. The address is wrong or does not exist. The most frequent cause, with a code such as 550 5.1.1.
2. Your message failed authentication. The receiving server checks SPF, DKIM and DMARC. If you send from your domain through a service that is not set up for it, the message can fail and be blocked. Some mailbox providers reject unauthenticated mail outright.
3. Your IP address or domain is on a block list. A blocklist is a database that receivers consult to refuse mail from sources linked to spam. See blocklist removal and delisting.
4. Poor sending reputation. A history of complaints, bounces or spam trap hits leads providers to block or throttle you. Our article on email reputation explains the signals.
5. Content looks like spam. Certain phrases, link patterns, attachments or image-only emails can trigger content filters.
6. Too much, too fast. A sudden burst from a new sender or a new IP address is limited. This may look like a temporary 4xx failure at first.
7. The recipient's policy. A company may block messages from outside, from certain countries, with certain file types or from free mail domains.
8. The recipient blocked you. A person can add your address to a block list in their own mailbox.
9. Message too large. See email size limits.
10. Technical faults in your setup: no reverse DNS on a sending IP, a mismatch between your sending hostname and your IP, or a missing TLS connection.

Common blocked-email messages and what they mean

Exact wording differs between providers, and we cannot list every variant. The reply text often contains a link to the provider's own help page for that code, and that page is the authority for what the provider means. Our guides to SMTP bounce codes and reading a bounce code show how to decode them.

How to fix a blocked email as an individual sender

1. Read the bounce and note the code and the text.
2. Check the recipient's address, including the domain.
3. Try a short plain message without attachments or links to the same address. If it gets through, the problem is the content or the size of the original.
4. Ask the recipient to check their spam folder and, in a company, to ask their administrator to check quarantine.
5. If you use a work or school account, ask your own administrator whether outbound filters held the message.
6. If you send from your own domain, check your domain's authentication. The free SPF, DKIM and DMARC checker is a quick first test.

How to fix blocked email as a business sender

1. Segment the failures. Group bounces by provider (Gmail, Microsoft, Yahoo and others) and by code. A block at one provider points to something specific to that provider's rules.
2. Check authentication. Confirm SPF, DKIM and DMARC pass, and that they align with your From domain. See authenticating your sending domain.
3. Check blocklists. Our free blacklist check looks up your sending IP across common lists. If you are listed, find the cause before you ask for removal, or you will be listed again.
4. Look at reputation tools. Google Postmaster Tools shows how Gmail sees your domain; see Google Postmaster Tools setup.
5. Review list quality. Remove addresses that bounce or never engage, and stop mailing purchased lists. A spam trap hit can trigger a block on its own.
6. Slow down. If you changed volume or a sending IP, ramp up gradually. See warming up a new domain or IP.
7. Check your content. Remove misleading subject lines, broken links and heavy image-only layouts. See the spam checker guide.
8. Contact the provider if it offers a way. Many large providers have a form for senders to request a review. Give them facts: your domain, the IPs you use, the error text and what you have changed. Do not expect an instant answer.

When the block is on the recipient's side

If you are the receiver and a message you expect never arrives, there are several places to look. Check spam, junk and any tabs. Check your quarantine if you use a company mail system. Look at your block list and your filters and rules. Ask the sender for the exact bounce text. Add the sender to your safe list; our guide on how to whitelist an email address shows how. If your organisation blocks the sender, the administrator can change it, but a good reason should come first.

How to avoid being blocked in future

• Send only to people who asked for your mail.
• Authenticate every sending domain, and keep DKIM on.
• Verify addresses at sign-up and before big sends. See email validation.
• Watch bounce, complaint and block rates, and act early. Our reputation monitoring helps you spot trends.
• Keep a steady sending pattern, and avoid sudden spikes.
• Give a clear way to unsubscribe, as in the one-click unsubscribe guide.
• Separate transactional mail from marketing, so that a marketing problem does not block receipts and password resets. See separating streams.

References and further reading

• RFC 3463: Enhanced Mail System Status Codes
• RFC 5321: Simple Mail Transfer Protocol
• RFC 7489: DMARC