Summary
Even when emails originate from a reputable vendor, their images can sometimes be blocked at the network level, beyond typical email client settings. This usually points to issues with the image hosting domain's reputation, the content delivery network (CDN) used, or stringent internal network security policies. It is a critical problem because it suggests the vendor's infrastructure or practices may be inadvertently triggering corporate firewalls or web filters, impacting deliverability and perception.
Key findings
- Network-level blocking: Images are blocked directly by the recipient's network or firewall, not merely suppressed by an email client setting. This means attempts to open the image URL in a browser also fail.
- Domain reputation: The reputation of the domain hosting the images (often a CDN) can lead to blocks. Even if the main email sending domain is reputable, a poorly managed CDN can cause issues. For more on this, see why third-party emails get rejected.
- CDN configuration: Vendors might use CDNs with generic or suspicious-looking subdomains, which some networks are configured to block proactively. This can be an intentional choice by the vendor that leads to problems.
- Security policies: Aggressive firewall or browser security policies within the recipient's network (e.g., at a company) can block content even from legitimate sources to minimize risk. Learn more about general reasons for email image blocking in this Mailmodo guide.
Key considerations
- Vendor accountability: A reputable email vendor should maintain practices that ensure their content, including images, is not blocked by common network security measures. This directly impacts your view of their service reliability.
- Branded links: Ensuring all links and image URLs are branded with the vendor's primary domain (or a well-known, dedicated subdomain) can significantly improve trust with network filters.
- CDN reputation management: Vendors need to actively monitor and manage the reputation of their image hosting domains and CDNs. For example, some WordPress image URLs can affect deliverability; see WordPress image URLs and Yahoo Mail.
- Internal IT consultation: It is advisable to consult your internal IT or security team to understand specific network blocking reasons, as they may have custom rules in place.
What email marketers say
Email marketers often face the challenge of images being blocked, even from trusted sources. Their perspectives highlight concerns about vendor reliability, the importance of proper email configuration, and the impact of technical choices on email deliverability. They emphasize that while some blocking is expected due to client settings, network-level blocks from reputable vendors indicate deeper issues that need addressing.
Key opinions
- Vendor accountability: Many marketers are frustrated when a vendor in the email space fails to pass their firewall restrictions, viewing it as a sign of poor practice.
- Unbranded links: A common complaint is when image hosting links are not branded with a CNAME to represent a subdomain of the parent domain, raising flags.
- Security vs. deliverability: While understanding IT's incentive to restrict system access for security, marketers also emphasize the need for vendors to ensure deliverability.
- Impact on perception: Images failing to load can make emails look broken and unprofessional, even if the issue is on the recipient's network.
Key considerations
- Direct URL testing: If images are blocked by your network, try accessing the image URL directly in a browser to confirm it is not just an email client setting. This is a common first step.
- Contact internal IT: Your internal IT department can provide insights into specific firewall or browser policies that may be causing the blocks.
- Vendor communication: Engage with your email vendor to understand their image hosting practices and urge them to improve their content deliverability for various network environments. It is important to know why your emails might be failing.
- Alternative text (Alt-text): Always ensure images have descriptive alt-text, which can convey the message even if images are blocked. This is a basic but essential workaround, as highlighted by Stripo.email.
Marketer view
Email marketer from Email Geeks observes that their network is blocking images from a reputable vendor, even when trying to access the image URLs directly in a browser. This suggests the issue is deeper than standard email client settings.
Marketer view
Email marketer from Quora indicates that security is a primary reason email clients block images, protecting users from embedded malicious code. This proactive blocking minimizes security risks even from seemingly legitimate sources.
What the experts say
Deliverability experts weigh in on image blocking by networks, often pointing to specific technical configurations and choices made by the sending vendor. Their insights reveal that many blocking issues stem from deliberate, albeit sometimes suboptimal, setup decisions, rather than pure random chance. They underscore the importance of proper CDN usage and careful domain naming for image hosting.
Key opinions
- Intentional configuration: Experts suggest that when a domain CNAMEs to a commercial CDN, the vendor made intentional choices about their image hosting, even if those choices lead to blocks.
- CDN policing: A CDN that does not adequately police its customers can contribute to a poor reputation, resulting in image blocking. This is crucial for overall domain reputation.
- Suboptimal domain naming: Using random-looking or 'ugly' domain names for image hosting, even if from a commercial CDN, can prompt network filters to block content.
- Decision-making failure: A series of questionable technical decisions by the vendor regarding their CDN setup and domain choice can significantly contribute to deliverability issues.
Key considerations
- Assess CDN choices: Vendors should carefully consider the reputation and practices of their chosen CDN providers, as this directly impacts their email deliverability.
- Consistent branding: Ensure that image hosting domains align with the primary sending domain to avoid triggering malicious content flags.
- Proactive monitoring: Regularly monitor your image and link domains for any signs of blocklisting (or blacklisting) or reputation issues that could affect loading.
- Vendor collaboration: If you are a recipient, provide specific examples to your vendor so they can investigate and optimize their image hosting practices. This can help prevent issues across multiple IP addresses.
Expert view
Deliverability expert from Email Geeks suggests testing if an image can be downloaded on a phone when not on Wi-Fi. This helps determine if the issue is network-specific rather than a general blocking problem.
Expert view
Deliverability expert from SpamResource explains that many spam filters block emails containing various elements, including images and links, especially if the sender is not explicitly trusted. This is a common defense mechanism.
What the documentation says
Official documentation and industry guides provide a clear rationale for why images are blocked and offer technical solutions. They highlight security as the paramount concern, protecting users from malware, tracking, and privacy breaches. Understanding these documented reasons helps in diagnosing and preventing image blocking issues, emphasizing standard practices like email authentication and responsive design.
Key findings
- Security and privacy: Most email programs block remote images by default to protect users from tracking pixels, web bugs, and malicious content. This is a fundamental security feature, not a bug.
- Bandwidth reduction: Blocking images reduces the initial size of the email, improving load times, especially for users on slower connections or mobile devices. Fastmail's documentation explains this.
- Sender trust: Images from trusted senders (e.g., those in your address book or safe sender list) are typically allowed to load automatically. Trust is built over time through consistent good practices.
- Email authentication: Proper implementation of email authentication protocols like SPF, DKIM, and DMARC is critical. If your mail server modifies messages before sending, it can lead to blocks. For more, see a simple guide to DMARC, SPF, and DKIM.
Key considerations
- Implement alt-text: Always include descriptive alt-text for all images, as this provides content even when images are blocked by default.
- Provide web version links: Offer a 'view in browser' or 'web version' link at the top of your emails so recipients can view the full content if images are blocked. Stripo.email suggests this.
- Optimize content balance: Maintain a healthy balance between text and images to ensure your message is conveyed even if images don't load. Excessive images can also trigger spam filters, a factor in why emails go to spam.
- Monitor deliverability: Regularly monitor your email deliverability rates and engage with tools like Google Postmaster Tools to identify potential issues before they become widespread.
Technical article
Documentation from Mailmodo states that email clients block images to protect users from security risks, such as malicious codes embedded in the content. This is a fundamental layer of defense.
Technical article
Documentation from Campaign Refinery explains that certain email clients, by default, block images for security and privacy. Recipients will need to click a 'Load Images' prompt to display them.
Related resources
14 resources
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