Why are images from a reputable vendor's email blocked by my network?

Email marketer from StackExchange suggests that the network's Intrusion Prevention System (IPS) might be falsely identifying the images as part of a zero-day exploit attempt, leading to the block. This can occur if the IPS signature database is outdated or overly sensitive.

Email marketer from Email Marketing Forum explains that if the vendor uses a Content Delivery Network (CDN) to host images, the CDN's IP reputation might be poor due to other users on the same CDN engaging in malicious activities. This could lead to your network blocking the entire CDN.

Email marketer from Email Deliverability Blog explains the vendor's sender reputation (related to the IP or domain sending the email) may be affecting image display if your email client or server is using filtering based on sender reputation, even if the vendor is generally considered reputable. This filtering might affect image loading.

Email marketer from Web Development Forums discusses the possibility of "mixed content" blocking if the email is sent over HTTPS but includes image URLs that are only served over HTTP. Some networks block mixed content to prevent security vulnerabilities.

Email marketer from Reddit suggests the network's content filter might be categorizing the image hosting domain as a potential risk, leading to the blocking. They also recommend checking the content filter settings or whitelisting the specific domain used for image hosting.

Marketer from Email Geeks suggests checking with IT for firewall or browser policy blocks. They also ask if the image hosting links are branded with a CNAME to represent a subdomain of the parent domain, suggesting extra scrutiny if so.

Email marketer from Infosec Community explains browser security settings or extensions might be blocking the images due to privacy or security concerns. This could be related to tracking prevention or aggressive ad-blocking features.

Email marketer from Spiceworks Community explains that the network might be blocking the images due to overly aggressive security policies or firewall settings. It suggests checking the firewall logs to see if the image server's domain or IP address is being blocked.

Email marketer from Network Engineering Forums suggests that DNS resolution issues could be preventing the network from resolving the hostname of the image server, leading to the block. This could be due to a DNS server outage or misconfiguration.

Email marketer from Cybersecurity Forums suggests if there are TLS/SSL certificate issues (e.g., expired or invalid certificates) on the server hosting the images, it could lead to browsers or network devices blocking the image loading for security reasons.

Expert from Word to the Wise explains that some networks and email clients use image proxies which can sometimes fail or misinterpret the vendor's image hosting setup. This is due to the network essentially acting as a man-in-the-middle, retrieving the images and then serving them to the recipient.

Expert from Email Geeks explains the vendor intentionally set up a CDN with a specific domain configuration (www.*.com) and a name that looks like word<randomstring>.com, implying a lack of oversight or disregard for potentially problematic configuration choices.

Documentation from Palo Alto Networks Documentation details how URL filtering works in their firewalls. The firewall checks the category and reputation of URLs. If the vendor's image hosting URL is categorized negatively or has a poor reputation, it will be blocked.

Documentation from Microsoft Support explains that Outlook has settings that control automatic image downloads. If "Don't download pictures automatically in HTML e-mail messages or RSS items" is enabled, Outlook may block images, even from reputable vendors.

Documentation from Cloudflare Support explains if the vendor has implemented hotlinking prevention measures on their image server, your network might be blocked from directly accessing the images, especially if the Referer header is not being correctly passed or if the vendor's CDN configuration is blocking requests without a proper referer.

Documentation from Cisco Documentation explains that web filtering solutions block content based on categories, reputation, and other criteria. The vendor's image server might be inadvertently categorized as malicious or undesirable by the web filter, leading to the block.

Documentation from Fortinet Document Library details the application control features of their firewall products. Application control can block specific types of content, including images from unknown or untrusted sources, even if they are delivered via email from a reputable vendor.