Compression4 min readUpdated 2026-04-05
How to Compress Images to Send via Gmail / Outlook Under 25MB
Jaswinder Singh
Image Optimization Specialist • PixEnhance Studio
At A Glance (Key Takeaways)
- Gmail, Yahoo Mail, and Apple Mail enforce a 25MB maximum attachment cap per email.
- Microsoft Outlook (Exchange) often enforces an even lower limit of 10MB to 20MB.
- Base64 email MIME encoding inflates physical file sizes by approximately 33%, meaning an 18MB file will frequently trigger a 25MB bounce error.
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The 33% Base64 Overhead Trap
Many users wonder why an email containing a 21MB attachment gets rejected with a "Message exceeds 25MB limit" error.
Email protocols cannot send raw binary data. They convert binary files into ASCII text using Base64 encoding, which expands the byte size by roughly one-third.
To ensure smooth delivery, always compress your photo attachments so their total size stays under 15MB.
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