When your mail does not arrive or you cannot send, the cause is almost always one of a few common issues: misconfigured DNS, a blocked sender, failed authentication, or a rejection by the receiving server. This guide walks you through how to diagnose each situation with Exact Hosting Hosted Email.
About Hosted Email spam protection
Exact Hosting uses a built-in spam protection system on the Hosted Email platform. It blocks the majority of unwanted mail automatically and adapts as you mark messages as spam or not spam. When a message is rejected, the rejection happens at one of two points, and how you troubleshoot depends on which.
SMTP rejects vs. bounceback rejects
Before you troubleshoot, work out which type of rejection you are dealing with:
| Rejection type | What happens | Where the rejection comes from |
|---|---|---|
| SMTP reject | Your mail client or webmail shows an error when you try to send. The message never leaves. | The Exact Hosting outbound server refused to accept the message. |
| Bounceback reject | The message sends successfully, but you later receive a "delivery failure" notification. | The recipient's mail server refused the message after it was sent. |
Step 1: Run the general troubleshooting checks
Start with these checks for any delivery problem, whether you can't send or can't receive.
| Check | What to verify |
|---|---|
| Confirm your MX records are correct. | Your domain's MX records must point to Exact Hosting's mail servers. If you are not sure of the correct values, see Configuring Email DNS Records and Mail Client Settings. |
| Confirm spam is being filtered, not rejected. | Make sure your account is set to deliver suspected spam to your Spam folder rather than reject it outright. |
| Confirm you are not blocking the sender. | Review your block list and webmail filters to make sure you have not blocked the sender's email address, domain, or IP address. The sending IP appears on the Received-SPF line of the original message headers. |
| Check SPF, DKIM, and DMARC results. | Review the message headers to confirm the sender's SPF, DKIM, and DMARC checks are passing. A failure on any of these is a common reason mail is rejected or filtered. |
Tip: Useful free tools for these checks include DMARC Analyzer's SPF checker and MxToolbox DMARC Lookup.
Step 2: Troubleshoot SMTP rejects (you cannot send)
If you get an immediate error when you try to send, check your account and message first.
| Check | What to verify |
|---|---|
| Check your account status. | Make sure your account is not suspended, that sending is enabled, and that you have not reached your daily outbound mail limit. |
| Review the message itself. | Save the message as a draft and review it. Would the content or recipient list look like spam to a receiving server? Make sure it follows the Exact Hosting Acceptable Use Policy. |
Step 3: Troubleshoot bounceback rejects (the receiving server refused the message)
If your message left Exact Hosting but came back as undeliverable, look at the bounce notification you received. The receiving server usually includes a reason, which points you to the fix.
Common bounce reasons:
- The recipient does not exist. Double-check the address for typos and confirm it with the recipient.
- The recipient's mailbox is full. Ask the recipient to clear space and try again.
- SPF, DKIM, or DMARC check failed. Confirm your domain's authentication records are configured correctly. See Setting Up SPF Records for Exact Hosting Email.
- Your sending IP is blocklisted. Contact Exact Hosting Support. Depending on the blocklist, we can investigate and, where possible, request delisting on your behalf.
Marking an email as spam
Marking a message as spam teaches the filter about the sender, headers, and content patterns so similar messages are caught in the future. Marking a message as not spam teaches the filter that the sender is safe.
- Select the message and choose Mark as spam.
- If prompted, click Accept to confirm.
Note: If you agree to share spam data with our partner, the consent prompt will not reappear. If you decline, you will be asked each time you mark a message as spam.
Tip: Marking a legitimate marketing email as spam has limited effect because those senders are already known. Use the Unsubscribe link in the email instead.
Common SMTP error codes
The error code on a rejection tells you whether the failure is permanent or temporary, and points to the likely cause.
5.x.x permanent failures
The message cannot be delivered as-is. Something must be corrected before it will send.
| Code | Meaning |
|---|---|
| 550 5.1.1 User unknown | The recipient address does not exist. Usually a typo. |
| 550 5.4.1 Relay access denied | The sender is not authenticated or not allowed to relay. |
| 552 5.2.2 Mailbox full | The recipient is over quota. |
| 553 5.1.2 Invalid recipient address | The address is malformed or the domain does not exist. |
| 554 5.7.1 Message rejected (content or policy) | A spam filter, blocklist, or security policy refused the message. |
4.x.x temporary failures
The receiving server expects to retry. These usually clear on their own.
| Code | Meaning |
|---|---|
| 421 4.3.2 Service not available | The receiving server is temporarily down or overloaded. |
| 450 4.2.0 Mailbox unavailable | The mailbox is temporarily unavailable, often during maintenance. |
| 451 4.3.0 Temporary server error | A spam check, DNS issue, or server resource problem. |
| 452 4.2.2 Insufficient system storage | The receiving server is out of disk space or resources. |
Authentication and security errors
| Code | Meaning |
|---|---|
| 535 5.7.8 Authentication credentials invalid | Wrong username or password for SMTP. |
| 530 5.7.0 Authentication required | The server requires authentication before relaying mail. |
| 550 5.7.26 Unauthenticated email not accepted | Usually a DMARC, SPF, or DKIM failure. |
| 554 5.7.9 Message not accepted for policy reasons | Blocked by DMARC enforcement or spam filtering. |
Connection and DNS errors
| Code | Meaning |
|---|---|
| 421 4.4.2 Connection dropped | The receiving server closed the connection unexpectedly. |
| 450 4.4.1 Host not found | DNS lookup failed for the recipient's domain. |
| 550 5.4.4 Routing loop detected | The message is stuck in a loop between mail servers. |
Tip: A 5.x.x code means something needs to be fixed before the message will send. A 4.x.x code usually clears on its own unless it persists.
Contacting Exact Hosting Support
If you have worked through these checks and still cannot resolve the delivery problem, contact Exact Hosting Support. To help us locate the message in our logs, include:
- Your account or domain name. The Exact Hosting account or domain the affected mailbox is on.
- The recipient email address. The address the message was sent to.
- The sender email address. The address the message was sent from.
- Date, time, and time zone of the failure. This helps us find the message in the logs.
- The full bounce message or SMTP error. Include all headers and codes.
Next steps
- Review your authentication setup. See Setting Up SPF Records for Exact Hosting Email and Understanding Gmail, Microsoft, and Yahoo DMARC Requirements for Hosted Email.
- Reduce spam scores on outbound mail. See Reducing Spam Scores When Sending Email.
- Read the headers of rejected messages. See Viewing Email Message Headers and Understanding Email Headers.
Questions? Contact Exact Hosting Support.
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