How to fix blocked emails and improve deliverability

Email blocking prevents legitimate messages from reaching their intended recipients. Your emails might bounce back with delivery failure notices, land in spam folders or disappear entirely without explanation. These blocks happen when spam filters flag your messages as suspicious based on content, sender reputation or technical configuration issues.

You will identify why your emails are being blocked and fix the underlying causes. This involves checking your domain reputation, configuring SPF records correctly, adjusting message content and understanding how spam filters evaluate your mail. Once resolved, your emails deliver reliably to recipient inboxes.

Understand how sender reputation affects delivery

Sender reputation determines whether mailbox providers accept your emails. This reputation score combines your domain age, sending patterns, spam complaints and the IP addresses your mail servers use. Newly registered domains start with lower reputation scores, which means sending large volumes of marketing emails immediately after registration often triggers blocks.

All mail sent from shared hosting passes through spam-filtering gateways that protect server IP reputation. These gateways examine every outbound message, assign a numeric spam score based on content and characteristics, and block messages that exceed the threshold. This system protects deliverability for all customers sharing the same mail infrastructure.

Check your domain reputation before investigating other causes. Visit the Barracuda Central reputation lookup and enter your domain. If your domain appears on blocklists, you need to request removal through the blocklist operator’s delisting process before your emails will deliver reliably.

Identify email blocks from bounce messages

Bounce messages confirm when spam filters block your emails. These automated responses arrive in your inbox shortly after sending and contain diagnostic information about why delivery failed.

1. Check your inbox for bounce messages.
   Look for emails with subjects like “Mail delivery failed: returning message to sender” or “Undelivered Mail Returned to Sender”. These indicate the receiving server rejected your message.
2. Review the message headers.
   Open the bounce message and locate the technical details section. This contains information about which spam filter blocked the message and why. Headers typically include spam scores, filter rules that triggered and specific content issues.
3. Note the recipient address and send time.
   Record which address you sent to and when you sent the message. Mail filter logs retain information for only a few days, so you need these details if you contact support for investigation.

Bounce messages provide the starting point for diagnosing delivery problems. The specific error codes and filter rules mentioned in headers guide you towards the correct fix.

Fix SPF record configuration

SPF records are DNS entries that list which mail servers can send email on behalf of your domain. Major mailbox providers like Gmail and Outlook check SPF records to verify messages come from authorised servers. Missing or incorrect SPF records cause authentication failures that trigger spam filters.

Hosting accounts automatically generate SPF records when created. However, if you use external DNS providers or custom nameservers, your SPF configuration might be incomplete or incorrect.

1. Verify your current SPF record.
   Use an SPF lookup tool to check your domain’s existing SPF record. Enter your domain name and review the results. The tool displays whether an SPF record exists and if it contains syntax errors.
2. Check your nameserver configuration.
   If you use external DNS providers, confirm your SPF record includes the correct mail server IP addresses. Our nameserver management guide explains how to verify and update DNS settings.
3. Add or update your SPF record.
   Follow our SPF record configuration guide to create or modify your SPF entry. The record must list all mail servers authorised to send email for your domain.
4. Wait for DNS propagation.
   DNS changes take up to 48 hours to propagate globally. Test your SPF record again after this period to confirm the changes applied correctly.

Correct SPF configuration prevents authentication failures and improves your sender reputation. Mailbox providers trust properly authenticated mail more than messages from domains without SPF records.

Remove spam trigger phrases from content

Spam filters analyse message content for patterns commonly found in unwanted mail. Certain words, phrases and formatting choices increase your spam score even when your message is legitimate. Multiple triggers in a single email compound the problem and push your spam score above blocking thresholds.

Review your email content and remove or rephrase these common spam triggers:

• Promotional language like “free offer”, “limited time” or “act now”
• Words or phrases in all capital letters, particularly in subject lines
• Multiple exclamation marks or excessive punctuation
• Generic greetings such as “Dear Customer” instead of personalised names
• Banking terms including “statement”, “invoice” or “account verification”
• Authentication requests like “sign in now”, “verify your account” or “confirm your identity”
• Unusual character spacing like “F R E E” or special Unicode characters

Some of these phrases appear in legitimate business communications. The problem occurs when multiple triggers combine in a single message. Rewrite your content to use natural language, specific details and professional formatting. Replace generic greetings with recipient names, use sentence case in subject lines and limit punctuation to standard usage.

Test links for phishing filter triggers

Phishing emails use deceptive links to imitate legitimate websites and steal credentials. Spam filters examine every hyperlink in your messages and block emails containing suspicious URLs. Your legitimate links might trigger these filters if they share characteristics with known phishing patterns.

1. Send a test message without links.
   Compose your email exactly as before but remove all hyperlinks. Send this version to the same recipient who received the blocked message. If this test delivers successfully, one of your links triggered the phishing filter.
2. Add links back individually.
   Send another test message containing only your first link. Wait for delivery confirmation, then send a second test with the next link. Continue this process until you identify which URL causes blocking.
3. Replace problematic links.
   Once you identify the triggering URL, check whether it uses URL shorteners, redirects or suspicious domains. Replace shortened links with full URLs, remove unnecessary redirects and ensure all links point to your own verified domains.

Phishing filters protect users from credential theft and malware distribution. Understanding how phishing attacks work helps you avoid patterns that trigger these protective measures in your legitimate communications.

Balance images and text content

Spammers hide message content from filters by using images instead of text. This tactic makes it difficult for spam filters to analyse message content, so filters treat emails with low text-to-image ratios as suspicious. Your legitimate marketing emails might trigger these filters if they contain mostly images with minimal text.

Maintain a healthy balance between text and visual content. Include at least 200-300 words of plain text for every image you add. Write descriptive paragraphs that explain your message rather than relying on images to convey information. This approach improves deliverability and makes your emails accessible to recipients using screen readers or blocking images by default.

Attachments raise similar concerns. Phishing emails often include malicious attachments disguised as invoices or documents. If you need to share files, consider linking to documents hosted on your website rather than attaching them directly to emails.

Manage email marketing campaigns properly

Email marketing campaigns generate spam complaints when recipients cannot unsubscribe or when you send to purchased lists. These complaints damage your domain reputation and place you on blocklists that prevent all your emails from delivering.

Follow these practices to maintain good standing:

• Only send marketing emails to recipients who explicitly opted in to receive them
• Include a clear unsubscribe link in every marketing message
• Process unsubscribe requests immediately, within 24 hours at most
• Never purchase email lists or send to addresses you collected without permission
• Monitor your spam complaint rate and investigate any increases

Check whether your domain appears on the Spamhaus blocklist. If listed, you must request removal through their delisting process and address the underlying issues that caused the listing. Our guide on setting up mailing lists covers proper configuration for marketing campaigns.

Troubleshooting persistent delivery issues

Some blocking issues require investigation beyond the common causes covered above. If you have addressed SPF records, content triggers, links and sender reputation but still experience blocks, deeper technical problems might exist.

Emails block with no clear cause

Spam filters use hundreds of rules that evaluate message characteristics. Your email might trigger obscure rules that are not immediately obvious from bounce messages or content analysis.

• Save the complete bounce message including all headers
• Note the exact time you sent the message (mail filter logs expire after a few days)
• Record both the sending and receiving email addresses
• Contact our support team with these details for log analysis

Blocks only affect specific recipients

If your emails deliver successfully to most recipients but consistently block for certain domains, the receiving mail server might maintain stricter filtering rules or have blocklisted your domain specifically.

• Check whether the recipient’s domain uses aggressive spam filtering
• Ask the recipient to check their spam folder and mark your messages as not spam
• Request that the recipient’s IT team whitelist your domain
• Consider using alternative communication methods for these specific recipients

Sudden blocking after months of successful delivery

Abrupt changes in deliverability often indicate your domain was added to a blocklist or your sending patterns changed dramatically. Recent increases in email volume, new types of content or compromised email accounts can trigger sudden blocks.

• Check all major blocklists for your domain and IP addresses
• Review recent changes to email content, volume or recipients
• Verify that no email accounts were compromised and used for spam
• Gradually reduce sending volume if you recently increased it

Further reading on email authentication

Email authentication extends beyond SPF records to include DKIM signatures and DMARC policies. These additional protocols work together to verify sender identity and prevent email spoofing. DKIM adds cryptographic signatures to your messages that receiving servers can verify, while DMARC tells receiving servers how to handle messages that fail authentication checks.

Major mailbox providers increasingly require proper authentication configuration. Gmail and Yahoo announced stricter requirements in 2024 that mandate DKIM and DMARC for bulk senders. Even if you send low volumes, implementing these protocols improves deliverability and protects your domain from spoofing attacks.

The DMARC.org overview explains how these authentication methods work together. Understanding the complete authentication stack helps you diagnose complex delivery issues and maintain strong sender reputation as email security standards evolve.

Wrapping up

Your emails now deliver reliably without triggering spam filters. You identified blocking causes through bounce messages, configured SPF records correctly, removed content triggers and established proper email marketing practices. Recipients receive your messages in their inbox rather than spam folders.

Monitor your email deliverability over the coming weeks. Check bounce rates, review any new spam complaints and verify that authentication records remain properly configured. Our shared hosting services include spam filtering and mail gateway protection that maintains server reputation for all customers.

If you run into any trouble, get in touch and our team will be happy to help.