Images and PDF attachments significantly influence email deliverability. While images aren't strictly necessary, their size, ratio to text, optimization for mobile, use of alt text, and hotlinking can trigger spam filters or negatively impact user experience. PDFs, especially large, password-protected ones, or those with suspicious content (like embedded code or ".com" in the name), raise red flags. Excessive attachment sizes also violate server limits. Consistent branding is also key. Ultimately, a holistic approach focusing on content relevance, file size, secure coding practices, and user experience is vital.
9 marketer opinions
The use of images and PDF attachments in emails can significantly impact deliverability. Factors such as image size, text-to-image ratio, image optimization for mobile, use of alt text, and hotlinking practices all play a role. Similarly, large, password-protected, or executable-code-embedded PDFs can trigger spam filters. Maintaining consistent branding and avoiding suspicious content within attachments are also crucial for ensuring positive engagement and avoiding deliverability issues.
Marketer view
Email marketer from Email on Acid explains that missing or irrelevant alt text for images can harm deliverability and accessibility. Providing descriptive alt text ensures that users with image loading disabled or using screen readers can understand the content, improving engagement and sender reputation.
8 May 2022 - Email on Acid Blog
Marketer view
Email marketer from Stack Overflow shares that embedding executable code or macros within PDF attachments significantly increases the risk of being flagged as spam, leading to deliverability problems. Avoid including such elements in PDFs attached to emails.
26 Jun 2024 - Stack Overflow
5 expert opinions
Experts generally agree that while images are not required for email deliverability, their use, along with PDF attachments, can affect it. Simply including a PDF isn't inherently an issue, but longer PDFs, those containing malware, or those with suspicious names (like including ".com") can cause problems. Embedding images as attachments can offer privacy benefits by preventing tracking, but larger message sizes may impact deliverability. Finally, it's crucial to ensure all attachments, including PDFs, are safe, relevant, and free of misleading content to avoid being flagged as spam.
Expert view
Expert from Email Geeks explains there is no need for an image in email for better deliverability.
25 Feb 2025 - Email Geeks
Expert view
Expert from Email Geeks responds to concerns about PDFs, clarifying that while they can sometimes be a deliverability issue (especially longer PDFs that might hide malware), the mere presence of a PDF isn't inherently problematic.
17 Dec 2024 - Email Geeks
4 technical articles
Technical documentation emphasizes that large images and PDF attachments significantly impact email deliverability. Exceeding server limits due to excessively large attachments can lead to delivery failures. A high volume of emails with primarily images (to bypass spam filters) can result in being flagged as spam. User-reported spam complaints about emails with large images or attachments can negatively affect sender reputation and thus, deliverability. Moreover, exceeding email message size limits, which images and PDFs contribute to, results in non-delivery.
Technical article
Documentation from Google Postmaster Tools indicates that high spam rates reported by users for emails containing large images or attachments can negatively affect your sender reputation and lead to deliverability issues.
10 Mar 2023 - Google Postmaster Tools
Technical article
Documentation from RFC 5321 defines technical specifications for email and states that excessively large attachments can lead to delivery failures due to server limitations and potential triggering of spam filters.
18 Aug 2021 - RFC 5321
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