Why Does Email Have a 25 MB Attachment Limit? Understanding PDF File Sizes

Have you ever tried to send a PDF by email and received a message saying that the attachment is too large?

If your PDF is larger than around 25 MB, you may find that some popular email services won't let you send it as a normal attachment.

But why is there a 25 MB limit? Why can't email simply allow 100 MB or 500 MB attachments?

The answer has to do with how email systems handle attachments, server storage, bandwidth, security, and the way files are encoded when they are sent through email.

Why Do Emails Have Attachment Size Limits?

Email was originally designed primarily for sending messages, not for transferring large files.

Modern email systems can handle attachments, but large files create additional challenges for email providers. Large attachments can:

• Consume more server storage
• Require more bandwidth
• Take longer to upload and download
• Increase processing requirements
• Create additional security and spam risks
• Make email synchronization more difficult

Because of these limitations, email providers generally impose attachment-size restrictions. The exact limit varies between providers.

Why Do People Talk About a 25 MB Limit?

The 25 MB figure is commonly associated with Gmail's attachment limit.

Gmail allows users to send attachments up to 25 MB in total in a message. This limit applies to the combined attachment size rather than necessarily meaning that every individual file can be exactly 25 MB.

If the total exceeds the service's limit, you may not be able to send the message with those attachments directly.

Other email providers may have different limits. Therefore, there isn't a universal 25 MB email limit for every email service.

Why Does a 20 MB PDF Sometimes Cause a Problem?

This is where things become interesting.

You might have a PDF that appears to be 20 MB on your computer, but the email system may process the attachment differently when sending it.

Email attachments are commonly encoded using Base64 so that binary files can be transported through systems designed around email message formats.

Base64 encoding increases the amount of data by roughly one-third. This means an attachment's effective size during transmission can be significantly larger than its original file size.

What Is Base64 Encoding?

Base64 is a method used to represent binary data as text.

PDFs, images, spreadsheets, ZIP files, and other binary files aren't naturally plain text.

Email systems historically relied heavily on text-based message formats, so attachments can be encoded into a text representation before being included in an email.

The encoding itself adds overhead. In simplified terms:

Original file → Base64 encoding → Larger email payload

The exact size increase depends on the encoding and the overall message structure, but Base64 adds approximately 33% to the encoded data.

Why Not Just Increase the Email Attachment Limit?

At first, increasing the limit might seem like an obvious solution.

However, email is a distributed system. A message travels through multiple servers and systems before reaching the recipient.

Large attachments can affect:

• Sending servers
• Receiving servers
• Mailbox storage
• Mobile synchronization
• Network bandwidth
• Spam and malware scanning
• Backup systems
• Email clients

If every email could contain hundreds of megabytes of attachments, the infrastructure requirements would increase considerably.

This is one reason email providers encourage users to use cloud-storage and file-sharing services for larger files.

What Happens When You Send a Large PDF?

Imagine you want to send a 40 MB PDF.

Your email provider may determine that the message exceeds its attachment limit. Instead of attaching the PDF directly, the service may offer another solution.

For example, Gmail can use Google Drive for larger files. The recipient receives a link rather than having the entire file embedded directly in the email.

This approach separates email communication from large-file storage and delivery.

Why PDFs Become So Large

Not every PDF is large. A simple text document might be only a few hundred kilobytes. However, PDFs containing images can become much larger.

High-resolution images

A PDF containing many high-resolution photographs can quickly become large.

Scanned documents

A scanned page is usually stored as an image inside the PDF. A 50-page scanned document can therefore be significantly larger than a digitally created text document.

Screenshots

Technical reports often contain screenshots of applications, websites, dashboards, and code. These images increase the document size.

Product catalogues

Businesses often create PDF catalogues containing dozens or hundreds of product photographs. These files can easily become large.

Presentations

PDF versions of PowerPoint or other presentations can contain large images, diagrams, and graphics.

How to Send a PDF Larger Than 25 MB

If your PDF is too large for direct email attachment, you have several options.

Option 1: Compress the PDF

The first option is to reduce the PDF's file size. Compressing a PDF can often drastically reduce its size.

If the resulting file falls within your email provider's attachment limit, you can attach it normally.

Option 2: Use Cloud Storage

If compression isn't enough, upload the PDF to an approved cloud-storage service and send the recipient a sharing link. This is often more practical for very large files.

Option 3: Split the PDF

If the recipient doesn't need the entire document at once, you can split the PDF into smaller files.

However, splitting a document isn't always ideal because it creates multiple files.

Option 4: Use an Approved File-Sharing Platform

Businesses may have their own approved file-sharing systems. For confidential or business-critical documents, use the platform recommended by your organization rather than an unfamiliar file-sharing service.

Why Compressing a PDF Can Be Better Than Splitting It

Suppose you have a 30 MB project report.

You could split it into two or three PDFs. But the recipient now has to download and manage multiple files.

If compression can reduce the document to 10 MB while keeping it readable, you can send a single file instead.

That creates a simpler workflow:

Large PDF → Compress → Check quality → Send

Does PDF Compression Reduce Quality?

It can, depending on how the PDF is compressed.

Compression generally involves a trade-off between file size and quality. A PDF containing mostly text may compress differently from one containing hundreds of photographs.

For business reports, invoices, contracts, and ordinary documents, moderate compression may provide a good balance.

After compression, always check:

• Text readability
• Images
• Charts
• Diagrams
• Page layout

The goal isn't necessarily to make the file as small as possible. The goal is to make it small enough while remaining useful.

How to Make a PDF Small Enough for Email

If your PDF is too large, follow this workflow:

1. Step 1: Check the current size. Right-click the PDF and check its file size.
2. Step 2: Identify unnecessary content. Remove pages or images that aren't required if appropriate.
3. Step 3: Compress the PDF. Use a PDF compression tool such as BunnyPDF.
4. Step 4: Check the result. Open the compressed PDF and verify its quality.
5. Step 5: Check the attachment limit. Confirm the maximum attachment size supported by your email provider.
6. Step 6: Send or share. If the file is within the limit, attach it to your email. If it is still too large, use an appropriate cloud-storage or file-sharing solution.

BunnyPDF: Compress Large PDFs Before Emailing

BunnyPDF can help when a PDF is too large to send conveniently through email.

Instead of splitting a document into multiple files, you can first try compressing it.

A simple workflow is:

Large PDF → BunnyPDF Compress PDF → Smaller PDF → Email

This can be useful for:

• Business reports
• Invoices
• Project documentation
• Scanned documents
• Product catalogues
• Portfolios
• Academic reports
• Presentations

Frequently Asked Questions

Conclusion

The 25 MB email limit isn't simply an arbitrary restriction.

Email systems need to handle storage, bandwidth, security scanning, message processing, synchronization, and compatibility across many different systems.

Large files can place additional demands on this infrastructure, which is why email providers set attachment limits.

If you have a PDF that's too large to send, you don't necessarily need to split it immediately. First, try reducing its size.

Compress → Check → Send

And if the PDF is still too large, consider using an approved cloud-storage or file-sharing service and sending the recipient a link instead.

For everyday PDF compression, BunnyPDF can be a convenient way to reduce large PDF files before sharing them.