How to Convert Files for Email: Reduce Size & Fix Format Issues

Why Email Attachments Fail (And How to Fix It)

You have prepared the perfect document, video, or image collection for a client or colleague, you hit send, and then the dreaded bounce-back arrives. The file is too large, the format is not supported, or the recipient cannot open what you sent. Email attachment failures waste time, delay projects, and create frustration on both ends.

The root cause is almost always one of two problems: the file is too big for the email provider's limits, or the file is in a format the recipient's system does not support. Both problems are solvable with the right conversion and compression approach.

This guide covers every type of file you might need to email -- documents, images, videos, audio, and archives -- with specific format recommendations, size targets, and step-by-step conversion instructions for each.

Email Attachment Size Limits

Every email provider enforces strict size limits on attachments. Exceeding these limits means your email will either bounce back or the attachment will be silently stripped.

The safest universal limit is 15 MB per email. Plan your file conversions and compression around this target.

Documents: The Most Common Email Attachments

Word Documents and PDFs

PDF is the gold standard for emailing documents. It preserves formatting across every device and operating system, cannot be accidentally edited, and is universally supported. If you are sending Word documents, converting to PDF first is almost always the right choice.

Convert Word to PDF:

Use the Word to PDF converter to create a clean PDF while preserving all formatting, images, and layout.

Reduce PDF Size:

Large PDFs -- especially those with embedded images, scans, or complex graphics -- can exceed email limits easily. The PDF compressor reduces file size by 50-90% while maintaining readability.

For scanned documents, the compression gains are particularly dramatic. A 15-page scanned contract might be 25 MB as a PDF but only 3-4 MB after compression.

Spreadsheets

Excel files can grow large quickly, especially with multiple sheets, charts, and embedded images. If the recipient only needs to view the data (not edit it), convert to PDF:

• Use the Excel to PDF converter for clean, paginated output
• Remove unnecessary sheets before converting
• Delete hidden data, comments, and revision history to reduce size

If the recipient needs an editable spreadsheet, save as .xlsx rather than .xls -- the newer format uses ZIP compression internally and is typically 30-50% smaller.

Presentations

PowerPoint files are notoriously large due to embedded images, videos, and animations. For email:

• If they need to present it: Compress images within PowerPoint (File > Compress Pictures) before sending
• If they just need to view it: Convert to PDF using the PowerPoint to PDF converter
• If it contains animations: Export as a video using MP4 format with H.264

Images: Choosing the Right Format and Size

Images are the second most common email attachment, and they are frequently too large. A single unedited photo from a modern smartphone is 5-15 MB. Four or five photos and you have exceeded most email limits.

Best Image Format for Email

The rule is simple: Use JPEG for photos and PNG for screenshots and diagrams. Everything else should be converted first.

Converting iPhone Photos (HEIC to JPEG)

iPhones save photos in HEIC format by default. While HEIC offers excellent compression, many Windows users and older email clients cannot open these files. Convert HEIC to JPEG before emailing using the HEIC converter.

Compressing Images for Email

For photos, the image compressor reduces file size while maintaining visual quality. Target these sizes:

• Viewing on screen: 200-500 KB per image (quality 80-85%)
• Printing at home: 500 KB - 1.5 MB per image (quality 90%)
• Professional printing: Do not compress -- use a cloud link instead

If you have many images, consider creating a ZIP archive instead of attaching each one individually. This also reduces the Base64 encoding overhead.

Videos: The Biggest Email Challenge

Video files are almost always too large for email attachments. A single minute of 1080p video is typically 100-300 MB -- far beyond any email limit. However, very short clips (under 30 seconds) can work with aggressive compression.

Making Video Small Enough for Email

Target: Under 15 MB for universal email delivery.

Step 1: Choose the right format

MP4 with H.264 video and AAC audio. No exceptions. This format offers the best compression-to-compatibility ratio. For more detail on why, the best video format for email guide covers the reasoning.

Step 2: Compress aggressively

Use the video compressor with these settings:

• Resolution: 720p (1280x720) -- adequate for email viewing
• Bitrate: 500-800 kbps for short clips
• Audio: 96-128 kbps AAC mono

Step 3: Trim unnecessary content

If your video has dead air at the beginning or end, trim it with the video trimmer. Every second you remove saves 50-100 KB.

FFmpeg command for email-sized video:

ffmpeg -i input.mov -c:v libx264 -crf 28 -preset slow -vf scale=1280:720 -c:a aac -b:a 96k -movflags +faststart email_video.mp4

When Video Is Too Large: Use a Link

For videos longer than 30 seconds or higher quality, use a cloud link instead:

1. Upload to Google Drive, Dropbox, or OneDrive
2. Generate a shareable link
3. Paste the link in your email body

This is how professionals handle video delivery. The cloud storage file formats guide covers which formats work best with each cloud service.

Audio Files

Audio files can be surprisingly large in uncompressed or lossless formats.

Audio Format Recommendations for Email

• MP3 at 128-192 kbps -- The universal choice for email audio. A 5-minute audio file is roughly 5-10 MB
• AAC at 128 kbps -- Slightly better quality than MP3 at the same bitrate, widely supported
• Avoid WAV and FLAC -- A 5-minute WAV file is about 50 MB; always convert before emailing

Convert audio files using the appropriate converter:

• WAV to MP3 converter for lossless-to-lossy conversion
• MP3 compressor to reduce the bitrate of existing MP3 files

For a detailed comparison of audio formats, the lossless vs lossy compression guide explains the quality tradeoffs.

Multiple Files: Archive and Compress

When you need to send several files, creating a ZIP archive offers multiple benefits:

1. Smaller total size -- ZIP compression reduces overhead
2. Single attachment -- Easier for the recipient to download and manage
3. Preserved folder structure -- You can organize files into folders
4. Reduced Base64 overhead -- One encoded attachment instead of many

Creating Efficient Archives

On macOS: Right-click the files > Compress

On Windows: Select files > Right-click > Send to > Compressed (zipped) folder

On Linux/Terminal:

zip -r files_for_email.zip folder_name/

For maximum compression:

zip -9 -r files_for_email.zip folder_name/

If the resulting ZIP is still too large, you need to compress individual files before archiving. Focus on the largest files -- images and documents typically offer the most compression gains.

Format Compatibility Quick Reference

Not every recipient can open every format. Before sending, consider what software the recipient has.

Checklist Before Hitting Send

Use this pre-send checklist to avoid email attachment failures:

1. Check total attachment size -- Keep under 15 MB for universal delivery
2. Use universal formats -- PDF for documents, JPEG/PNG for images, MP4 for video, MP3 for audio
3. Compress where possible -- A few minutes of compression can prevent delivery failures
4. Test with yourself first -- Send the email to yourself to verify attachments open correctly
5. Consider cloud links for large files -- Anything over 10 MB is safer as a link
6. Name files clearly -- Use descriptive filenames, not "IMG_4532.jpg" or "Document1.pdf"
7. Mention attachments in the body -- Tell the recipient what you have attached and what software they need

Related Resources

• Best Video Format for Email -- Deep dive into video email attachments
• How to Convert Word to PDF -- Detailed Word-to-PDF guide
• How to Reduce PDF File Size -- PDF compression techniques
• Optimize Images for Website -- Image optimization principles that also apply to email
• How to Batch Convert Files -- Processing multiple files at once

Summary

Email attachment success comes down to two things: keeping files under the size limit and using universally compatible formats. PDF for documents, JPEG for photos, PNG for screenshots, MP4 for short videos, and MP3 for audio. When in doubt, compress first and use a cloud link for anything that does not fit comfortably within a 15 MB budget. Taking two minutes to convert and compress before sending saves both you and your recipient time and frustration.