Email attachment limits are one of those things everyone runs into but few people know precisely. The limits vary by provider, by the recipient's system, and sometimes by corporate IT policy. Knowing the numbers โ and what to do when your PDF exceeds them โ saves the frustration of a bounced message or a delivery failure you find out about too late.
Attachment Limits by Email Provider
These are the sending limits for the most common providers as of 2025. Note that hitting the sending limit doesn't guarantee delivery โ the recipient's server may impose its own lower limit.
- Gmail: 25MB per message (total, including all attachments). Files over 25MB automatically prompt you to share via Google Drive instead.
- Outlook.com / Hotmail: 20MB per message for web and app. Files above this are automatically uploaded to OneDrive and shared as a link.
- Yahoo Mail: 25MB per message.
- Apple iCloud Mail: 20MB. Larger files can be sent via Mail Drop (up to 5GB), which uploads the file to iCloud and sends the recipient a download link.
- Corporate / business email (Microsoft 365, Google Workspace): typically 25-35MB, but IT administrators can set this lower. Some organizations cap attachments at 10MB or even 5MB for security reasons. If you're regularly hitting limits with business contacts, their IT policy may be more restrictive than the provider default.
The Hidden Complication: Email Encoding Adds Size
Email attachments are encoded in Base64 format before transmission, which increases the size by approximately 33%. A PDF that's 18MB on disk becomes roughly 24MB as an email attachment. This means a 19MB PDF โ safely under Gmail's 25MB limit on disk โ may actually exceed the limit when encoded for sending.
The practical rule: to reliably send under a 25MB limit, your PDF should be under 18MB on disk. To send under a 20MB limit, keep the file under 14MB. This encoding overhead is why compression to "just under" the limit sometimes still fails.
What to Do When Your PDF Exceeds the Limit
In order of simplicity:
- Compress first: run the PDF through WukongPDF's PDF Compression tool at www.wukongpdf.com. Medium compression on a typical business document reduces size by 50-70% with no visible quality change. This is the fastest fix for most cases.
- Share via cloud storage: upload to Google Drive, Dropbox, or OneDrive and send a link instead of an attachment. No size limit, the recipient can access it immediately, and you can update the file if needed.
- Split the document: if the PDF has natural sections, split it and send the relevant part only. A recipient who needs pages 5-12 of a 40-page report doesn't need the whole document.
- Use a file transfer service: WeTransfer, Filemail, and similar services handle large files up to several GB and generate a download link the recipient can use without any account.
The Worst Case: Silent Delivery Failure
Most email systems notify the sender when an attachment is too large to deliver. But some corporate mail filters silently drop large attachments โ the email appears to send successfully, the recipient receives the message, but the attachment is missing. Neither party gets an error message.
For important documents, ask the recipient to confirm they received the attachment โ not just the email. A quick reply confirming the PDF arrived takes thirty seconds and prevents the situation where a contract or deliverable goes missing in transit without anyone knowing.