How does domain blocking in some countries affect email deliverability and image rendering?

Key findings

• localized impact: Domain blocking directly affects email deliverability and accessibility for recipients within the specific blocked countries. If the domain is unreachable, so are your emails.
• global deliverability: Unless the blocking indicates a broader, global reputation issue, it generally does not impact email deliverability in countries where the domain is not blocked.
• dns resolution issues: Blocking at the DNS level means that crucial email authentication mechanisms like SPF, DKIM, and DMARC may fail, as recipient servers cannot perform necessary lookups. This is discussed in our simple guide to email authentication.
• image rendering: Images hosted on a blocked domain or its subdomains will likely not render in emails for users in affected regions, significantly impacting email presentation.
• domain reputation: While local blocking doesn't automatically tank global reputation, consistently failing to deliver in specific regions might indirectly signal issues. Learn more about understanding your email domain reputation.

Key considerations

• monitor regional deliverability: Regularly check deliverability metrics for target countries that might have blocking policies.
• optimize image hosting: Consider using content delivery networks (CDNs) with globally distributed servers to host email images, minimizing reliance on a single potentially blocked domain. Learn more about CDN hosted images and deliverability.
• robust authentication: Ensure your SPF, DKIM, and DMARC records are correctly set up and align. These protocols are critical for email authentication and can be disrupted by DNS blocking.
• content design: Design emails to be effective even without images. Ensure all critical information is conveyed through text.
• understand local regulations: Familiarize yourself with internet and email policies in key target countries. MarTech offers insights into what marketers need to know about email deliverability.

Key opinions

• localized delivery failure: Marketers frequently observe that emails simply will not get through to recipients in countries where the sending domain is blocked at a national level.
• image display problems: A common concern is that if email images are hosted on a blocked domain, they will not load, leading to a broken or incomplete email experience. This is critical for protecting deliverability for image-only emails.
• minimal global impact: Most marketers believe that country-specific domain blocking does not severely affect deliverability outside of those particular regions, provided overall sender reputation is healthy.
• website access issues: If users cannot access the linked website due to blocking, the purpose of the email campaign is undermined, even if the email is delivered.
• reputation is key: Marketers stress the importance of maintaining a strong general sending reputation to prevent widespread deliverability issues, as highlighted by Mailmunch's email deliverability tips.

Key considerations

• alternative image hosting: Explore options for hosting images on domains that are less likely to be blocked, or use CDNs. Consider how self-hosting affects deliverability.
• text-based email design: Prioritize text content to ensure the core message is delivered even if images fail to load. This also includes making sure email images deliver and experience well.
• geographic segmentation: Segment email lists by country to track and address specific deliverability challenges in blocked regions.
• monitoring engagement: Pay close attention to open rates and click-through rates in affected countries to gauge the true impact of blocking.

Key opinions

• dns blocking impact: Experts agree that if a domain is blocked at the DNS level in a country, email authentication (SPF, DKIM, DMARC) for emails sent to that country will likely fail, leading to non-delivery. This impacts deliverability rates and technical solutions.
• mx lookup failures: If a recipient server attempts an MX lookup to verify a sender's domain and it fails due to country-level blocking, the email will not be delivered.
• localized effect: The impact of such domain blocking is generally confined to the specific countries enforcing the block, not affecting global deliverability if the sender's reputation is strong elsewhere.
• image rendering risk: Experts confirm that images hosted on a domain or subdomain blocked in a country will likely not display, depending on how the blocking is implemented. This affects how images in emails affect deliverability.
• commercial services exception: A caveat is that major commercial email services operating within a blocked country might be compelled to obey local restrictions, potentially extending the impact.

Key considerations

• proactive dns monitoring: Routinely check DNS resolution for your sending domain from various global locations, especially in countries with known internet restrictions.
• strong authentication: Ensure your email authentication records (SPF, DKIM, DMARC) are always valid and accessible, as they are a first line of defense against blocking related to DNS issues.
• localized testing: Conduct specific deliverability tests to the affected countries or regions to understand the precise impact. Our email deliverability test checklist can help.
• image content strategy: Develop strategies for image delivery, potentially by hosting images on regionally diverse CDNs or using a separate, unblocked domain for image hosting.
• global reputation management: Focus on maintaining excellent sender reputation across all global operations to minimize any spillover effect from localized blocking, as detailed in this guide on the ultimate guide to email deliverability.

Key findings

• dns resolution criticality: Core internet protocols, including those for email and web content, fundamentally rely on successful DNS resolution to translate domain names into IP addresses. If DNS lookups for a domain are blocked, associated services fail.
• authentication dependency: Email authentication protocols like SPF, DKIM, and DMARC require DNS queries to verify sender legitimacy. Domain blocking that interferes with DNS renders these checks ineffective, often leading to mail rejection.
• content loading mechanics: Images embedded in HTML emails are loaded via HTTP requests to their source domains. If the image-hosting domain is blocked, these requests will fail, preventing images from displaying.
• nation-state filtering: Many countries implement sophisticated internet filtering systems that can specifically target and block access to certain domains for their citizens.
• reputation system signals: While domain reputation is generally global, sustained local blocking can generate specific signals for ISPs that might influence their filtering decisions for that region.

Key considerations

• internet standards compliance: Adherence to all relevant internet and email standards (RFCs) is fundamental for maximizing deliverability, even when facing external blocking.
• redundant infrastructure: Utilize robust and globally distributed infrastructure, such as CDNs, for hosting email assets to improve resilience against regional blocking.
• diagnostic tools: Employ tools that can diagnose DNS resolution issues and network accessibility from various points worldwide to pinpoint blocking effectively.
• content fallback: Implement HTML email design practices that provide graceful degradation, ensuring content readability even when images do not load.
• policy awareness: Stay informed about the internet policies and filtering mechanisms employed by different nation-states that could affect email traffic.