Media files — images, GIF animations, PDF documents, and other attachments — make email campaigns more informative and engaging. But placing them incorrectly can cause problems: slow loading, display glitches, blocking by mail providers, and even loss of subscriber trust.

In this guide, we'll cover how to safely and correctly place media files and attachments in emails, so they look perfect without hurting deliverability.

Why it matters to place media files correctly

  • Fast email loading on any device
  • Correct media rendering across different providers
  • Minimizing the risk of landing in spam
  • Safety for the recipient
  • A better user experience

Step 1. Choose the right file format

  • JPG/JPEG — photos, background images
  • PNG — logos, icons, images with transparency
  • GIF — simple animation (note: we don't compress GIFs)
  • PDF, DOCX, XLSX — documents, instructions, presentations (when attachments are needed)

Avoid using: MP4, WebP, AVI, ZIP — video and archive files are often blocked by mail providers.

Step 2. Optimize image size

Letteros has a built-in compression service, similar to TinyPNG, that automatically reduces the size of PNG and JPEG files without losing quality. This reduces the email's weight and speeds up loading.

Key rules:

  • Letteros doesn't compress GIF files — reduce them manually beforehand.
  • Keep the total weight of the email with media files (excluding attachments) under 1–1.5 MB.
  • A single image shouldn't exceed 500–600 KB.

Step 3. Host files on secure storage

  • Use HTTPS for all links.
  • Store files on reliable services (for example, via S3 or a corporate CDN).
  • Use Letteros's built-in storage for images.
  • Avoid obscure or suspicious domains.

Step 4. Add alt text to every image

  • Make emails accessible to users with disabilities.
  • Help readers understand the email's content if images fail to load.
  • Improve your sender reputation.

Step 5. Specify image dimensions in the code

  • Set width and height in the HTML.
  • For responsiveness, use max-width and height: auto.

Step 6. Don't embed media as attachments unless necessary

  • For images, always insert links instead of attaching the files.
  • Use attachments (PDF, DOCX) only when they're genuinely needed:for example, an instruction manual, a commercial proposal, or a price list.

Attachment limits:

  • File size: usually up to 5–10 MB (depends on the ESP and mail provider).
  • File types: only safe formats (PDF, DOCX, XLSX) — no ZIP, EXE, or MP4.
  • Number of attachments: keep it minimal (ideally 1–2 files).
  • Mention the attachment directly in the email body so it doesn't raise suspicion.

Step 7. Don't embed video or audio directly

  • Replace video with an image featuring a "Play" button that links to your website or YouTube.
  • Host audio files on an external resource and link to them instead.

Step 8. Test emails before sending

  • Check how the email renders in Gmail, Outlook, Yahoo, Apple Mail, and other clients.
  • Use the testing tools built into Letteros.
  • Check media loading speed and make sure all links work.

Step 9. Monitor deliverability

  • Track complaints, unsubscribes, and spam filters.
  • Use UTM tags to analyze the effectiveness of your media.
  • Maintain a balance between text and images (aim for at least 500–700 characters of text per email).

Conclusion

Placing media files and attachments safely helps boost engagement, preserve a good sender reputation, and ensure your emails actually get delivered. Letteros already has built-in tools for image optimization, so you have every chance to put together a professional-level campaign without extra hassle.

If needed, I can put together a checklist or template for your team. Just let me know!