How to improve email delivery rates to corporates blocked by Symantec?
Matthew Whittaker
Co-founder & CTO, Suped
Published 8 May 2025
Updated 18 Aug 2025
7 min read
Dealing with email delivery issues to large corporations, especially when they use robust security solutions like Symantec (now Broadcom), can be a significant challenge. These systems are designed to protect their networks from threats, and sometimes legitimate emails get caught in the crossfire. It can be particularly frustrating when vital transactional emails, like signup confirmations, fail to reach their intended recipients.
Many factors contribute to corporate email blocking, ranging from sender reputation to content specifics and technical configurations. I often see cases where companies struggle to pinpoint the exact cause because these systems operate with complex, layered rules. The goal is always to deliver value and secure communications, but the side effect can be overzealous filtering.
To ensure your emails land in the inbox and not the spam folder, it's crucial to understand how these corporate filters work and adopt a comprehensive strategy. We need to look beyond surface-level issues and dig into the technical underpinnings, sender reputation, and email content to effectively improve deliverability.
Understanding Symantec's filtering
When your emails are blocked by a corporate recipient using Symantec (or similar solutions), it's often due to their robust filtering mechanisms. These systems are designed to detect and prevent a wide range of threats, from spam and phishing to malware. They analyze multiple data points to assess the legitimacy of incoming mail.
Symantec's filtering primarily relies on a combination of IP address reputation, domain reputation, and content analysis. If your sending IP address or domain has a poor reputation, or if your email content triggers their spam filters, your emails are likely to be blocked or sent to the junk folder. This is why a comprehensive approach is necessary, as detailed in our guide on what causes Symantec email blocks.
The Network Prevent: Block SMTP Message action within Symantec's Data Loss Prevention (DLP) solution is a good example of how they can outright block messages. This typically occurs when an email triggers a policy violation, such as containing sensitive information or being associated with known spam patterns. You can find more details on these actions directly from Broadcom's technical documentation.
Understanding Symantec's filtering
Symantec's Email Security.cloud is a comprehensive service that includes advanced anti-spam and anti-malware features. Its effectiveness relies on multiple layers of protection, including sender reputation, content analysis, and policy enforcement. Understanding these layers is key to improving your deliverability.
The service analyzes billions of emails daily to identify and block threats, which means any deviation from best practices can lead to your emails being flagged. Familiarizing yourself with Symantec's anti-spam effectiveness issues and policies can provide deeper insights into their blocking criteria.
Key authentication protocols
One of the most critical steps to improving email delivery rates, especially to corporate networks, is ensuring your email authentication protocols are correctly set up. This includes SPF, DKIM, and DMARC. These records act as digital signatures that verify your emails are legitimate and prevent spoofing, which in turn builds trust with receiving mail servers.
Symantec, like other major email providers, heavily relies on these protocols to determine email legitimacy. A properly configured DMARC record, for instance, tells receiving servers how to handle emails that fail SPF or DKIM checks, instructing them to quarantine or reject suspicious messages. This demonstrates a commitment to email security that corporate filters appreciate. You can learn more about these protocols in our simple guide to DMARC, SPF, and DKIM.
Implementing a DMARC policy with a reporting address (RUA and RUF) is also crucial. These reports provide valuable insights into your email authentication failures, allowing you to identify and fix issues that might be causing blocks. Ongoing DMARC monitoring helps maintain consistent email deliverability.
Sender reputation and content quality
Beyond technical configurations, your sender reputation plays a massive role in whether your emails reach corporate inboxes. This reputation is built over time based on factors like bounce rates, spam complaints, and engagement metrics. A low reputation, whether for your IP or domain, can lead to widespread blocking by sophisticated filters like Symantec's. We delve into improving this in our guide on email reputation and deliverability.
For transactional emails, like confirmation emails, using a dedicated IP address can offer more control over your sending reputation compared to a shared IP. While shared IPs can be cost-effective, their reputation is influenced by other senders, potentially leading to blocks if others on the same IP engage in problematic sending behavior. However, it's not always an IP issue; sometimes, it's the domain reputation, especially if there's any perceived abuse like aggressive cold emailing.
Shared IP addresses
Cost-effective: Often included with email service provider plans.
Reputation volatility: Deliverability can be affected by other senders on the same IP.
Warm-up not needed: IPs are usually pre-warmed.
Dedicated IP addresses
Full control: Your sending reputation is solely yours.
Requires warm-up: You must build its reputation gradually.
Higher cost: Often an add-on or requires a higher-tier plan.
Content quality also affects deliverability. Even transactional emails can trigger spam filters if they contain spammy keywords, excessive links, or poorly formatted HTML. Ensure your emails are concise, relevant, and free of anything that could be misinterpreted as marketing spam. This is especially true when sending solicited business proposals, where clarity is key.
Troubleshooting and ongoing monitoring
When facing blocks from Symantec or any corporate filter, your first step should always be to identify the specific reason for the block. This means analyzing your bounce messages, which often contain error codes or descriptions from the receiving server. These messages are invaluable for diagnosing the root cause. You might find a message like "550 #5.1.0 Address rejected" indicating a policy block, or something more specific to reputation.
Check your sending IP and domain against common email blocklists (or blacklists). While Symantec maintains its own proprietary lists, many corporate filters also consult public blocklists. Being listed on a major blocklist can significantly impact your deliverability across multiple corporate domains. Our in-depth guide to email blocklists can help you understand this process.
Consistent monitoring of your deliverability metrics, including bounce rates and complaint rates, is paramount. This proactive approach allows you to detect issues early, before they escalate into widespread blocking. If you identify a Symantec block, reaching out to their support or the recipient's IT department with relevant email headers and bounce messages can often help resolve the issue. There are also community forums where users discuss these challenges, such as the Broadcom community discussion on Symantec.cloud blocks.
Views from the trenches
Best practices
Maintain meticulously clean email lists and promptly remove invalid or inactive addresses to minimize bounces.
Consistently monitor your email metrics, including open rates, click-through rates, and complaint rates, for early detection of issues.
Regularly check your domain and IP address against major email blocklists (or blacklists) to ensure you are not listed.
Use a dedicated IP address for transactional emails to have greater control over your sender reputation and avoid impact from other senders.
Common pitfalls
Ignoring bounce messages and delivery failure notifications, which contain crucial diagnostic information.
Aggressively sending cold emails from your primary domain, which can severely damage your domain's reputation with corporate filters.
Failing to implement or correctly configure email authentication protocols like SPF, DKIM, and DMARC.
Sending emails with generic or spammy content that can trigger sophisticated corporate spam filters.
Expert tips
Always retrieve and analyze the specific error messages provided by Symantec to understand the exact reason for blocking.
Consider segmenting your email sends; use different domains or subdomains for transactional versus marketing emails.
If using a new dedicated IP, warm it up gradually by sending small volumes of email first and slowly increasing over time.
Engage with the recipient's IT department, if possible, to get whitelisted or understand their specific filtering policies.
Expert view
Expert from Email Geeks says that corporate blocking is typically more IP-based, emphasizing the importance of a clean IP reputation for deliverability.
February 18, 2020 - Email Geeks
Expert view
Expert from Email Geeks observes less IP-based blocking and more domain-level blocking at the corporate level, particularly when sales teams are sending high volumes of cold emails.
February 18, 2020 - Email Geeks
Final thoughts on corporate email deliverability
Improving email delivery rates to corporates blocked by Symantec (or any advanced filter) requires a multi-faceted approach. It's not just about one fix, but a combination of solid technical foundations, a strong sender reputation, and diligent monitoring. By implementing robust authentication, maintaining clean lists, crafting relevant content, and actively troubleshooting, you can significantly enhance your chances of reaching the inbox.
Symantec (now Broadcom), can be a significant challenge. These systems are designed to protect their networks from threats, and sometimes legitimate emails get caught in the crossfire. It can be particularly frustrating when vital transactional emails, like signup confirmations, fail to reach their intended recipients.
