An email may sometimes fail to reach its recipient even though the sender's Internet connection, email password, Outlook configuration, and recipient address are all correct.

One common delivery failure reported by Gmail and Google Workspace servers is:

552 5.3.4 Your message exceeded Google's message size limits.
https://support.google.com/mail/?p=MaxSizeError

The error may also appear inside Microsoft Outlook as a Non-Delivery Report, commonly known as an NDR, bounce message, or delivery failure notification.

A typical notification may look similar to:

Your message did not reach some or all of the intended recipients.

The following recipient(s) cannot be reached:

recipient@example.com

552 5.3.4 Your message exceeded Google's message size limits.
gsmtp

The exact wording can vary, but the important information is:

552 5.3.4

and

MaxSizeError

This article explains what the error means, why it frequently occurs while forwarding emails, how attachment encoding affects message size, how to diagnose the problem, and the safest ways to send large files.

What Does SMTP Error 552 5.3.4 Mean?

SMTP is the protocol used by email servers to transmit messages.

When a receiving mail server returns:

552 5.3.4

it means the server has permanently rejected the current email because it exceeded one of its applicable message-size related limits.

Google's SMTP documentation currently lists several conditions that may result in 552 5.3.4, including:

• Overall message size exceeding Google's limit.
• Too many attachments.
• Total attachment-related limits being exceeded.
• Message headers becoming too large.
• An individual email header becoming too large.

Therefore, the full text accompanying the error is important when troubleshooting.

For the commonly seen:

552 5.3.4
Your message exceeded Google's message size limits
MaxSizeError

the most likely cause is that the transmitted email became too large.

Gmail Attachment Size Limit

For personal Gmail accounts, Google states that Gmail allows up to 25 MB of attachments in a message.

When multiple files are attached, their combined attachment size must remain within the applicable limit.

For larger files, Google recommends sending the file using Google Drive instead of transmitting it as a traditional attachment.

For managed work or education accounts, Google Workspace administrators may also configure applicable sending and receiving restrictions.

However, an important technical point is often overlooked:

The attachment size shown in Windows Explorer or Outlook is not necessarily the final SMTP message size.

Why Can a 20 MB or 22 MB File Still Cause a Size Error?

Email attachments do not travel through SMTP exactly as they exist on the computer.

Binary files such as:

• PDF
• JPG
• PNG
• DOCX
• XLSX
• ZIP
• MP4
• PPTX

must normally be converted into a format suitable for transmission inside an email message.

This is typically performed using MIME encoding, often with Base64 encoding for binary attachments.

Base64 makes the transmitted representation larger than the original file.

A rough technical estimate is:

Encoded Size ≈ Original File Size × 1.33

For example, a 20 MB binary file could require approximately:

20 × 1.33 ≈ 26.6 MB

before considering additional message content.

The complete email may also contain:

• Message headers
• HTML formatting
• Plain-text alternative body
• Inline logos
• Signature images
• Tracking graphics
• Previous conversation history
• Embedded images
• Additional attachments
• MIME boundaries and metadata

Therefore, the actual message transmitted through SMTP can be substantially larger than the file size visible to the user.

Attachment Size vs Total Message Size

These terms should not be confused.

Attachment size

This is the size of the actual files you attach.

Example:

Proposal.pdf       12 MB
Catalogue.pdf       8 MB
PriceList.xlsx      3 MB
-------------------------
Total              23 MB

Total email message size

The final SMTP email also contains:

Email headers
+
Message body
+
HTML content
+
Signature
+
Embedded graphics
+
MIME structure
+
Encoded attachments
+
Forwarded conversation data

Therefore:

Attachment size ≠ transmitted email size

This is one reason an email appearing to contain less than the nominal attachment limit may still be rejected somewhere along the mail-delivery path.

Why Forwarded Emails Frequently Cause MaxSizeError

Forwarding is one of the most common situations where this problem occurs.

Suppose you receive an email containing:

PDF attachment
Product catalogue
Company logo
HTML signature
Several embedded images
Previous correspondence

When you click Forward, Outlook may include much of that content again in the newly generated message.

The forwarded email may therefore contain considerably more data than expected.

This can be especially problematic when a long email thread has repeatedly been:

Sent
↓
Replied
↓
Forwarded
↓
Replied
↓
Forwarded again

The message can gradually accumulate:

• Old signatures
• Embedded logos
• Inline images
• Tracking pixels
• Previous attachments
• HTML formatting
• Long conversation history

Eventually, the resulting message can exceed the receiving server's limit.

Example Scenario

Suppose an incoming email contains:

PDF Proposal:          14 MB
Product Catalogue:      7 MB
Embedded images:        1 MB
Other content:        0.5 MB

Visible content appears to total approximately:

22.5 MB

After MIME/Base64 encoding and email overhead, the actual transmitted message may become significantly larger.

If the receiving infrastructure accepts a lower maximum message size, the message can be rejected with an SMTP error such as:

552 5.3.4

Why Outlook May Allow You to Click Send

Users sometimes ask:

If the email is too large, why did Outlook allow me to send it?

Because several separate systems participate in email delivery.

The sequence is generally:

Microsoft Outlook
        ↓
Outgoing SMTP server
        ↓
Internet mail routing
        ↓
Recipient mail server
        ↓
Recipient mailbox

Outlook may successfully submit the message to an outgoing server.

However, the destination Google server can still reject it.

The sender subsequently receives an NDR informing them that delivery failed.

This does not necessarily indicate a fault in Outlook.

Does 552 5.3.4 Mean the Recipient Mailbox Is Full?

Usually not.

This is an important distinction.

Google documents:

552 5.2.2

for certain recipient storage-related conditions, whereas:

552 5.3.4

is used for message-size, attachment-count, and message-header related limits.

Therefore:

552 5.2.2

May indicate a recipient storage problem.

552 5.3.4

Generally indicates a problem with the message being transmitted rather than simply an ordinary full-mailbox condition.

Always read the complete SMTP response because SMTP codes can have provider-specific explanatory text.

How to Diagnose Gmail 552 5.3.4

Step 1: Read the Complete Bounce Message

Look for:

552 5.3.4

and surrounding text such as:

Your message exceeded Google's message size limits

or references to:

MaxSizeError

If the message specifically mentions size, investigate attachments and message content first.

Step 2: Check Every Attachment

In Outlook, inspect the forwarded message and list all attachments.

Example:

Attachment	Size
Proposal.pdf	11 MB
Catalogue.pdf	9 MB
Images.zip	6 MB
Total	26 MB

In this example the attachments alone are already large enough to require another delivery method for a typical Gmail message.

Step 3: Check Hidden or Inline Content

Some email content does not appear as a conventional attachment.

Examples include:

• Company logos
• Signature graphics
• Social-media icons
• Embedded screenshots
• Background graphics
• Inline photos

These elements also contribute to message size.

Step 4: Check Whether It Is a Forwarded Email

If the problem occurs while forwarding:

1. Create a completely new email.
2. Copy only the required text.
3. Attach only the files actually needed.
4. Send it again.

If the new email succeeds, the original forwarded message probably contained excessive historical or embedded content.

Step 5: Remove Attachments and Test

Forward the same message but remove all attachments.

If it is delivered successfully, the attachments or combined message size were likely responsible.

Step 6: Send Attachments Separately

If there are multiple large attachments, divide them into separate messages.

Instead of:

Email 1
Attachment A
Attachment B
Attachment C
Attachment D

use:

Email 1
Attachment A
Attachment B

and:

Email 2
Attachment C
Attachment D

This can solve the problem when the aggregate attachment size is too high.

Best Solution: Send Large Files Through Google Drive

For files that are close to or above the email attachment limit, cloud sharing is generally preferable.

Google specifically recommends Google Drive for files too large to attach directly.

The workflow is:

Upload file to Google Drive
        ↓
Configure appropriate sharing permission
        ↓
Copy/share the Drive link
        ↓
Insert link into email
        ↓
Send a lightweight email

Advantages include:

• Much smaller email message.
• Lower chance of SMTP rejection.
• Easier delivery of large files.
• Files can be updated without resending a huge attachment.
• Access permissions can be controlled.
• Recipients can download the file when required.

Other Cloud Alternatives

Depending on organizational policy, files may also be shared through:

• Microsoft OneDrive
• Microsoft SharePoint
• Dropbox
• Secure client portal
• Managed file-transfer service
• Company cloud storage

For confidential business information, always use an approved corporate sharing service and appropriate permissions.

Compress the File Before Sending

Compression may help when the file is only slightly above the required size.

Common approaches include:

PDF → Optimize or Reduce File Size
Images → Resize or lower resolution
Documents → Remove unnecessary embedded images
Video → Re-encode at lower resolution/bitrate
Multiple files → Create ZIP archive

However, ZIP compression does not substantially reduce files that are already compressed.

For example:

• JPG
• MP4
• ZIP
• modern PDF files

may see little reduction.

Compress PDF Files

Large PDFs frequently contain high-resolution scans.

To reduce their size:

1. Open the PDF using an appropriate PDF editor.
2. Select an option such as Optimize PDF or Reduce File Size.
3. Lower unnecessary image resolution.
4. Save the optimized copy.
5. Verify that text remains readable.
6. Attach the optimized version.

A 30 MB scanned PDF can sometimes be reduced considerably without materially reducing readability, depending on its content.

Resize Images Before Emailing

Modern cameras and smartphones can produce photographs several megabytes each.

Ten such photographs may quickly produce a very large email.

Instead of sending full-resolution originals when they are not required, consider reducing dimensions.

For ordinary screen viewing, images usually do not require camera-original resolution.

Always retain original files separately when image quality is important.

Remove Attachments Before Forwarding

When the recipient only needs the text of an email:

1. Click Forward.
2. Remove all unnecessary attachments.
3. Delete unnecessary historical text if appropriate.
4. Send only the required information.

This is one of the simplest fixes for a MaxSizeError caused by forwarding.

Create a New Message Instead of Forwarding

Forwarded messages may contain substantial hidden HTML and MIME data.

For problematic messages:

1. Create a new email.
2. Enter the recipient.
3. Use a short new subject.
4. Copy only the important text.
5. Attach only essential files.
6. Send.

This produces a much cleaner email structure.

Can a Large Signature Cause the Problem?

Yes, although a signature alone is less commonly the sole cause of an overall message-size rejection.

Poorly designed email signatures may contain:

• Large PNG logos
• High-resolution JPG photographs
• Multiple icons
• Animated GIFs
• Embedded banners

A 2 MB signature repeated throughout a long conversation can contribute significant overhead.

Business signatures should therefore use properly optimized images.

Can the Email Subject Cause 552 5.3.4?

Potentially, yes.

Google currently documents 552 5.3.4 not only for message-size conditions but also for certain message-header size limits, including situations where headers or a Subject header are excessively large.

This is much less common than an oversized attachment, but it is important when troubleshooting unusual cases where:

• The email has no large attachment.
• The body is small.
• The bounce message explicitly mentions headers.
• The Subject header is abnormally large or malformed.

Always use the explanatory text after the SMTP code to identify which 552 5.3.4 condition occurred.

Can Too Many Attachments Cause 552 5.3.4?

Yes.

Google's SMTP error documentation includes a 552 5.3.4 condition where the number of attachments exceeds an applicable limit.

Therefore, troubleshooting should consider both:

Size of attachments

and:

Number of attachments

If hundreds or unusually large numbers of small files must be transferred, place them in an approved archive or cloud folder instead of attaching them individually.

Understanding MIME and Base64 Encoding

Email was originally designed primarily for text.

Modern email uses MIME — Multipurpose Internet Mail Extensions — to carry:

• HTML
• Images
• Documents
• Audio
• Video
• Binary files

Binary files commonly need encoding before being incorporated into an SMTP message.

Base64 represents binary information using text-safe characters.

Conceptually:

Binary attachment
        ↓
Base64/MIME encoding
        ↓
Larger email representation
        ↓
SMTP transmission

This explains why administrators should not calculate mail-flow capacity solely from Windows file sizes.

What Is GSmtp?

Some Gmail bounce messages end with:

gsmtp

This indicates that the response was generated by Google's SMTP infrastructure.

It is not itself an error code.

The meaningful troubleshooting information appears before it, for example:

552 5.3.4

along with the accompanying description.

Is SMTP Port 587 the Problem?

Generally, no.

A message-size error can appear while sending through:

smtp.gmail.com
Port 587
STARTTLS

but the presence of port 587 does not imply that the port is faulty.

If authentication works and the server accepts the connection but rejects the message for size, changing ports will not solve the underlying issue.

Instead, reduce the message size or use a file-sharing service.

Do Not Confuse Message Size with Mailbox Storage

These are completely different limits.

Mailbox storage

Controls how much total data can exist in a mailbox/account.

Example:

Mailbox used: 12 GB
Storage quota: 30 GB

Message-size limit

Controls how large a single transmitted email can be.

A recipient can therefore have plenty of free storage and still reject an individual oversized message.

Conversely, a very small email may fail if the recipient account has a storage problem.

Always troubleshoot the actual SMTP response.

Sender Limit vs Recipient Limit

Email delivery depends on both parties.

An email may pass the sender's server but fail at the recipient's server.

For example:

Sender allows 30 MB
Recipient allows 20 MB

Result:

Message rejected by recipient

Likewise, an organization can place stricter rules on its mail gateway than the underlying cloud provider.

Administrators should therefore check:

• Sending server limits
• Receiving server limits
• Mail security gateway limits
• Spam-filter limits
• SMTP relay limits
• Google Workspace settings
• Third-party email-security appliances

Recommended Troubleshooting Flow

Use the following workflow whenever you encounter a MaxSizeError:

Receive 552 5.3.4
        ↓
Read complete SMTP description
        ↓
Does it mention message size?
        ↓
Check attachment sizes
        ↓
Check forwarded content
        ↓
Check inline images/signatures
        ↓
Remove unnecessary attachments
        ↓
Create a fresh message
        ↓
Compress large files
        ↓
Still too large?
        ↓
Upload to Google Drive/approved cloud storage
        ↓
Send sharing link

If the response instead explicitly mentions header size or attachment count, investigate that condition rather than assuming the problem is only attachment bytes.

Best Practices for Business Email Attachments

For reliable business email delivery:

1. Avoid sending attachments close to the maximum permitted size.
2. Use cloud links for large PDFs, videos, backups, and presentations.
3. Compress scanned PDFs before sending.
4. Resize unnecessarily large images.
5. Remove old attachments when forwarding messages.
6. Keep email signatures lightweight.
7. Avoid repeatedly forwarding huge conversation chains.
8. Use a new message when a thread has become excessively large.
9. Check recipient-server restrictions.
10. Use approved secure file-sharing platforms for confidential data.

Administrator Troubleshooting

If users repeatedly receive 552 errors, administrators should examine the complete message headers and server logs.

Check:

Sender
Recipient
Timestamp
Message-ID
SMTP response
Attachment count
Attachment types
Raw message size
MIME structure
Mail gateway logs
SMTP relay logs

If Google Workspace is involved, also review:

• Gmail routing configuration
• Compliance rules
• Attachment policies
• SMTP relay configuration
• Security gateway configuration
• Administrative sending/receiving limits where applicable

Do not increase limits blindly. Large-message restrictions protect infrastructure performance and reduce abuse.

What Not to Do

Do not repeatedly click Send without modifying the email.

A permanent SMTP 5xx response means retrying the identical message is unlikely to solve the condition.

Also avoid:

• Renaming a large file without reducing it.
• Changing SMTP ports merely because the email is large.
• Reinstalling Outlook for a clear server-side size rejection.
• Deleting emails from the recipient mailbox unless the bounce specifically indicates storage exhaustion.
• Disabling antivirus because of a MaxSizeError.
• Assuming every 552 code means the same thing.

Read the complete enhanced status code and server explanation.

Quick Resolution

If you need the fastest practical solution:

Method 1 — Remove unnecessary attachments

Forward the message again after deleting large or unnecessary attachments.

Method 2 — Send the files separately

Divide multiple files across several messages.

Method 3 — Compress the files

Optimize PDF files, resize images, or create an archive where useful.

Method 4 — Use Google Drive

Upload the large file and send a sharing link.

Google explicitly recommends Drive for files that exceed Gmail's attachment size limit.

Method 5 — Create a fresh email

Instead of forwarding a very long email chain, create a clean new message containing only the information that the recipient requires.

Frequently Asked Questions — FAQ

1. What does Gmail error 552 5.3.4 mean?

It means Google rejected the email because an applicable message-size, attachment, or header-related limit was exceeded. The accompanying text identifies the specific condition.

2. What does MaxSizeError mean?

MaxSizeError indicates that the email being transmitted exceeded an applicable Google message-size limit.

3. Is 552 5.3.4 caused by a full recipient mailbox?

Not ordinarily. Google documents 552 5.2.2 for certain recipient storage problems, while 552 5.3.4 is associated with message-size, attachment-count, and header-limit conditions.

4. What is Gmail's attachment limit?

Google states that personal Gmail accounts can send attachments totaling up to 25 MB. Larger files should generally be shared using Google Drive.

5. Can multiple attachments together exceed the limit?

Yes. Google states that if multiple attachments are used, their combined size must remain within the applicable attachment limit.

6. Why does a file below 25 MB sometimes fail?

The final SMTP message includes more than the original file. MIME/Base64 encoding, HTML, signatures, inline images, headers, and other content all contribute to the transmitted size. In addition, managed environments or receiving systems may impose different limits.

7. Why does forwarding an email increase its size?

Forwarding can preserve old attachments, inline images, signatures, HTML formatting, and previous conversation history.

8. Will ZIP compression solve the problem?

Sometimes. It works well for compressible data, but JPG, MP4, ZIP, and many modern PDF files may already be compressed and therefore may shrink only slightly.

9. Can I send a large file using Google Drive?

Yes. Google recommends Drive for files larger than the normal attachment limit.

10. Will changing SMTP port 587 to another port solve 552 5.3.4?

No, not when the server explicitly rejects the message for size. The message must be reduced or transferred by another method.

11. Can Outlook itself cause the error?

Outlook may generate a large MIME message, particularly while forwarding attachments or HTML content, but the 552 response normally comes from the SMTP infrastructure that rejected the resulting message.

12. Can a large email signature cause delivery problems?

Yes. High-resolution logos, banners, GIFs, and repeated signature graphics can increase the final email size.

13. Does deleting old messages from the recipient inbox fix it?

Not if the error is 552 5.3.4 due to message size. Mailbox storage and individual message-size limits are separate.

14. Can sending fewer attachments help?

Yes. Google also documents 552 5.3.4 for attachment-count limits in certain situations.

15. Can a very large Subject line cause this error?

Google documents 552 5.3.4 for certain message-header size violations, including Subject-header conditions. Check the exact explanatory text returned with the bounce.

16. Is the 25 MB limit always identical for Google Workspace accounts?

Not necessarily. Google states that administrators of managed work and school accounts can control applicable attachment sending and receiving limits.

17. What is the easiest solution for a 40 MB PDF?

Upload the PDF to Google Drive or another approved secure file-sharing platform and email the sharing link.

18. What does "gsmtp" at the end of an error mean?

It indicates that the SMTP response originated from Google's mail infrastructure. The preceding SMTP status code and descriptive text are what should be used for troubleshooting.

19. Should I resend the same failed email repeatedly?

No. A 5xx SMTP response represents a permanent failure for that particular delivery attempt. Modify the message—usually by reducing its size—before trying again.

20. What should an IT administrator check if this keeps happening?

Check raw message size, attachment count, MIME structure, inline content, SMTP logs, mail-gateway policies, Google Workspace configuration, relay restrictions, and the recipient's mail-server limits.

Conclusion

The 552 5.3.4 MaxSizeError is primarily an email transport limitation rather than a general Outlook, password, Internet, or mailbox problem.

When the accompanying error says:

Your message exceeded Google's message size limits

the correct approach is to examine the complete size of the email—not merely the visible attachment size.

Remember:

Original file size
        +
MIME/Base64 encoding
        +
HTML email content
        +
Signatures
        +
Embedded images
        +
Previous forwarded content
        +
Message headers
        =
Actual transmitted email size

For routine business use, avoid pushing email attachments close to their maximum limits. Compress large files where appropriate, remove unnecessary attachments from forwarded messages, and use Google Drive or another approved cloud-sharing platform for larger data transfers.

This produces more reliable delivery, reduces mailbox congestion, and prevents repeated 552 5.3.4 MaxSizeError bounce messages.

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