Summary
When choosing between embedding and hosting email signature images, marketers face distinct trade-offs in deliverability, display reliability, and security. Embedded images are part of the email's content, ensuring more consistent display across clients, but they significantly increase email file size, which can negatively impact deliverability by triggering spam filters or causing images to appear as attachments. Conversely, hosted images are external assets that keep email size smaller, potentially aiding deliverability. However, they are frequently blocked by default in most email clients, including Gmail and Outlook, due to security and privacy concerns, such as preventing tracking or malicious content, leading to broken or absent image displays for recipients. While embedded images offer reliable visual consistency, hosted images present risks related to recipient privacy and unpredictable display, requiring recipients to manually enable image downloads. Marketers must weigh these factors based on their specific campaign goals and recipient base.
Key findings
- Embedded Images Increase Size and Deliverability Risk: Embedded images are part of the email's MIME structure, significantly increasing overall email file size. This larger size can negatively impact deliverability by increasing the chance of being flagged by spam filters and can sometimes cause images to appear as attachments, especially in older Outlook versions.
- Hosted Images Face Default Blocking: Hosted (or linked) email signature images are external assets. Most major email clients, including Gmail and Outlook, block these by default for security and privacy reasons, preventing tracking, malicious content, and IP address revelation. This often results in broken image displays unless the recipient manually enables image downloads.
- Hosted Images Pose Privacy and Security Risks: From a security perspective, hosted images can act as 'web beacons' or 'tracking pixels,' revealing recipient IP addresses and potentially enabling recipient tracking. This is a primary reason why email clients block them by default.
- Display Consistency vs. Deliverability Trade-off: There is a fundamental trade-off: embedded images offer more reliable visual consistency as they are part of the email content, but they incur deliverability risks due to increased size. Hosted images keep email size down, potentially aiding deliverability, but their display is highly unreliable due to default blocking.
- Embedded Images Common in Business Communications: While rare in bulk marketing emails, embedded images in email signatures are still common in person-to-person business communications due to their consistent display, though they can sometimes be misidentified by overly cautious security software.
Key considerations
- Email File Size: Consider the impact of email file size on deliverability and loading times. Embedded images increase size, potentially triggering spam filters, while hosted images keep email size smaller, which generally aids deliverability.
- Image Display Reliability: Assess the importance of consistent image display for your brand. Embedded images offer more reliable and consistent display across email clients, whereas hosted images are frequently blocked by default, leading to broken visuals.
- Recipient Security and Privacy: Prioritize recipient privacy and security. Hosted images carry privacy and security risks due to tracking capabilities and potential for malicious content, leading many email clients to block them. Embedded images do not carry these specific risks.
- Spam Filter Sensitivity: Factor in how spam filters might react. Larger emails with embedded images can sometimes be viewed with suspicion by ISPs, increasing the likelihood of being flagged as spam. Hosted images generally face less scrutiny from spam filters regarding size.
- Internal Security Policies: Be aware of internal security team concerns. Some organizations may have strict policies against external asset linking due to security risks, which could impact the choice of hosted images for internal communications.
What email marketers say
11 marketer opinions
Marketers navigating email deliverability must carefully consider the impact of email signature images, specifically the choice between embedding and hosting. Embedded images, directly included within the email, reliably display across clients but notably increase email size, potentially hindering deliverability by flagging spam filters or appearing as attachments. In contrast, hosted images, linked externally, maintain a smaller email size, which can benefit deliverability. However, their primary drawback is widespread default blocking by email clients due to significant privacy and security concerns, such as enabling recipient tracking, often resulting in an unappealing broken image display for recipients. This fundamental trade-off means prioritizing reliable visual branding might increase deliverability hurdles, while optimizing for email size risks an inconsistent brand presentation.
Key opinions
- Embedded Images and File Size: Embedded images are integrated directly into the email's MIME structure, which significantly increases the overall email file size. This can negatively impact deliverability, making emails more susceptible to spam filters and occasionally causing images to display as attachments, particularly in older email clients like Outlook.
- Hosted Images Face Default Blocking: Hosted images, being external assets, are frequently blocked by default across many major email clients, including Gmail and Outlook. This blocking mechanism is primarily a security and privacy measure, preventing tracking, malicious content, and the revelation of recipient IP addresses.
- Display Reliability Trade-off: While embedded images generally offer more dependable visual consistency because they are part of the email content, hosted images present a stark display challenge as they often appear as broken links or do not load at all unless the recipient manually enables image downloads.
- Hosted Image Security Risks: From a security perspective, externally linked email signature images can function as 'web beacons' or 'tracking pixels,' potentially exposing recipient IP addresses and allowing senders to track email opens and user behavior, which is a major reason for default image blocking by email clients.
- Core Deliverability Impact: The core decision involves a trade-off: embedded images prioritize consistent display but risk higher email size and potential deliverability issues, whereas hosted images maintain a smaller email footprint, which aids deliverability, but are prone to being blocked, compromising visual integrity and brand impression.
Key considerations
- Email Size and Deliverability: Evaluate the impact of email size on deliverability: Larger emails with embedded images are more likely to be flagged by spam filters, while hosted images help maintain a smaller email size, which is generally beneficial for inbox placement.
- Image Display Consistency: Prioritize image display reliability: If consistent brand presentation is paramount, embedded images offer more dependable display across various email clients, whereas hosted images often appear broken due to default blocking.
- Recipient Privacy and Security: Consider recipient privacy and security: Be aware that hosted images can be used for tracking purposes, revealing recipient IP addresses, a major reason for their default blocking by email clients. Embedded images do not pose these same privacy concerns.
- Internal Security Policies: Assess the potential for internal security conflicts: For corporate or internal communications, external asset linking through hosted images might conflict with an organization's security policies, leading to internal blocking or alerts.
- Visual Integrity vs. Deliverability: Weigh the trade-off between visual integrity and deliverability: Decide whether a consistently displayed signature (embedded) is worth the increased email size and potential deliverability challenges, or if a smaller email size (hosted) is preferable despite the risk of images not loading for recipients.
Marketer view
Marketer from Email Geeks explains that attached or embedded images are part of the message via MIME, while remotely linked images are hosted externally.
12 Jul 2024 - Email Geeks
Marketer view
Marketer from Email Geeks explains that hosted images can be hosted anywhere and are not required for reputation or deliverability purposes. They note that attached/embedded images are rare in bulk emails, and provide an example of their own corporate logo being hosted on Amazon for their email signature.
26 May 2024 - Email Geeks
What the experts say
2 expert opinions
The method of incorporating email signature images, whether embedded directly or hosted externally, carries significant consequences for email deliverability and security. Embedded images offer consistent display but increase the email's size, which Internet Service Providers often view with suspicion, raising the likelihood of the message being flagged as spam. Conversely, externally hosted images help maintain a smaller email footprint, generally encountering less scrutiny from spam filters due to size. However, their major drawback is frequent default blocking by email clients, primarily for security and privacy reasons like preventing open tracking, meaning recipients might not see these images without enabling them. This highlights a critical balance between ensuring visual presence and navigating spam filters and recipient privacy.
Key opinions
- Embedded Images and Spam Risk: Embedded images substantially increase email size, which Internet Service Providers may view with suspicion, elevating the likelihood of the email being classified as spam and hindering deliverability.
- Hosted Images and Deliverability: Remotely hosted images contribute to a smaller email footprint, which generally leads to less scrutiny from spam filters concerning message size, potentially benefiting deliverability.
- Display Reliability of Embedded Images: Embedded images are less prone to default blocking by email clients, ensuring a more consistent and reliable display of the signature image in the recipient's inbox without requiring manual action.
- Default Blocking of Hosted Images: Externally hosted images are frequently blocked by default across a wide range of email clients, primarily due to security and privacy concerns, meaning recipients often won't see them unless they manually enable image downloads.
- Tracking Capabilities of Hosted Images: Hosted images can enable email open tracking, revealing recipient IP addresses and user behavior, which is a significant factor contributing to their widespread default blocking by email services.
Key considerations
- Email Size Impact on Filtering: Evaluate how the overall email size, significantly increased by embedded images, might influence spam filter decisions and ultimately, inbox placement. Smaller email sizes typically encounter less scrutiny from filters.
- Image Blocking Likelihood: Consider the high probability of externally hosted images being blocked by default in many email clients, directly impacting the visual presentation and brand impression for recipients.
- Security and Privacy Implications: Assess the security and privacy risks associated with hosted images, particularly their capability for open tracking and IP address revelation, which often leads to their default blocking by email clients.
- ISP Scrutiny Levels: Understand that Internet Service Providers may apply varying levels of scrutiny based on the image embedding method, with larger emails containing embedded images often facing higher suspicion than those with smaller, hosted images.
- Recipient Experience: Prioritize the recipient's experience by balancing the desire for a consistently displayed signature image with the reality that hosted images may not load without manual intervention, potentially detracting from the email's visual integrity.
Expert view
Expert from Spam Resource explains that embedded images, commonly used in email signatures, pose deliverability risks as they increase email size and are viewed with suspicion by many ISPs, often leading to them being classified as spam. In contrast, remotely hosted images typically face less scrutiny from spam filters.
5 Mar 2025 - Spam Resource
Expert view
Expert from Word to the Wise shares that while embedded images in email signatures avoid default image blocking by email clients, they significantly increase email message size, which can be an issue for some ISPs. Conversely, externally hosted images allow for open tracking, but are frequently blocked by default for security and privacy reasons, meaning recipients might not see the signature image unless they enable it.
16 Nov 2024 - Word to the Wise
What the documentation says
4 technical articles
The choice between embedding and hosting email signature images presents a clear dilemma regarding display reliability versus deliverability and security. Most major email clients, including Gmail and Outlook, routinely block external images by default, primarily to safeguard user privacy and security from tracking or malicious content. This directly affects hosted signature images, which often appear broken or are entirely absent unless recipients manually enable them. Conversely, embedded images are typically displayed without such intervention, offering superior visual consistency, but they notably increase email file size, a factor that can sometimes negatively influence email deliverability by raising spam filter scrutiny.
Key findings
- Default Blocking of Hosted Images: Major email clients, including Gmail and Outlook, are configured to block externally hosted images by default. This is a fundamental security and privacy measure, aimed at preventing tracking and malicious content.
- Embedded Images Display Reliably: Embedded email signature images, being an integral part of the email's content payload, are generally displayed without being blocked by default, offering consistent visual presentation to recipients.
- Security Reasons for Blocking: The primary reasons for email clients blocking hosted images are security and privacy concerns, specifically to prevent tracking pixels from revealing recipient IP addresses and email open behavior, as well as to mitigate risks from potentially malicious external content.
- Recipient Experience with Hosted Images: Recipients of emails with hosted signature images will frequently see broken image icons or a blank space instead of the intended graphic, as they must often manually enable image downloads for these external assets to display.
- Embedded Images Increase File Size: While offering reliable display, embedding images directly into an email signature significantly increases the email's overall file size. This can potentially negatively impact deliverability by triggering spam filters or increasing email loading times.
Key considerations
- Prioritize Display Consistency: For email signatures where consistent visual display is crucial, embedding the image is generally the most reliable method, as it bypasses the default blocking common to most email clients for hosted images.
- Recipient Privacy & Security: Acknowledge that email clients block hosted images to protect recipient privacy and security. While hosted images reduce email size, they introduce tracking possibilities that many recipients and email services actively avoid.
- Impact on Deliverability Trade-off: Weigh the deliverability benefits of a smaller email size (with hosted images) against the high probability of the signature image not displaying versus the deliverability risks of a larger email (with embedded images) despite their consistent display.
- Alternative Text for Hosted Images: If choosing hosted images, implement effective alt text for your signature images. This ensures recipients still receive descriptive information, even if the image does not load by default.
- Consider Audience & Email Client Trends: Research your target audience's most commonly used email clients and their default image-handling settings. This insight can help inform whether the risk of image blocking for hosted content is acceptable.
Technical article
Documentation from Google Help explains that Gmail blocks external images by default to protect users from malicious content and tracking, which means hosted email signature images may not display unless the recipient explicitly allows them. Embedded images, being part of the email itself, are generally displayed without this blocking.
21 Feb 2024 - Google Help
Technical article
Documentation from Microsoft Support highlights that Outlook automatically blocks external images in emails to protect user privacy and security from malicious content or tracking. This directly impacts hosted email signature images, which will not display by default, whereas embedded images, being part of the email's content, are typically visible without user intervention.
26 Apr 2025 - Microsoft Support
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