The 552 5.2.3 error means your email exceeds the recipient’s mail server size limit — also known as “message length exceeds administrative limit” or “message too large.”
Fix it by compressing attachments, using cloud storage links (Google Drive, OneDrive, Dropbox), or splitting large files across multiple emails.
Unlike quota errors (where the mailbox is full), 552 5.2.3 targets the individual message size.
The recipient might have plenty of storage — your single email simply exceeds what their server accepts per message. Re-sending without reducing size guarantees another bounce.
Quick skim — 552 5.2.3 error overview
The 552 5.2.3 error indicates your message payload exceeds the receiving server’s per-message limit.
| Attribute | Details |
| Error code | 552 5.2.3 |
| Category | Message size / administrative limit |
| Meaning | Email exceeds the maximum allowed message size |
| Severity | Permanent (requires message modification) |
| Common causes | Large attachments, multiple files, base64 encoding overhead |
| Fix approach | Compress → use cloud links → split into parts |
What does message size exceeded mean?
Mail servers enforce per-message size limits to prevent resource exhaustion. When your email (body + attachments + encoding overhead) exceeds the limit, the server rejects it outright.
Why attachments appear larger
Email attachments use base64 encoding, which increases file size by approximately 37%. A 20 MB file becomes roughly 27 MB after encoding — potentially exceeding a 25 MB limit even though the original file seems small enough.
| Original Size | After Encoding | Result |
| 15 MB | ~20.5 MB | Usually passes |
| 20 MB | ~27.4 MB | Exceeds 25 MB limits |
| 25 MB | ~34.2 MB | Fails most providers |
Common provider limits
Different providers enforce different caps (and the lower of sender vs recipient limits applies):
| Provider | Limit | Notes |
| Gmail | 25 MB | Total message including encoding |
| Outlook.com | 20 MB | Per message |
| Microsoft 365 | 25-150 MB | Configurable by admin |
| Yahoo | 25 MB | Total size |
| Exchange On-Prem | Variable | Admin-configured |
Why does the 552 5.2.3 error occur?
Several scenarios push messages beyond server limits.
Large attachments
The most common cause — attaching files (videos, high-resolution images, design files, databases) that exceed limits after encoding.
Multiple attachments
Individual files may fit within limits, but their combined size (plus encoding overhead) exceeds the cap. Ten 2 MB files equal 20 MB raw — approximately 27 MB encoded.
HTML signatures with images
Complex email signatures containing embedded images add hidden bulk. Each inline image encodes separately, accumulating size.
Server mismatch
Your mail server accepts large messages, but the recipient’s server has stricter limits. The rejection happens at the receiving end.
How do you fix message size exceeded?
Reducing payload size resolves the immediate bounce. Multiple approaches work depending on your situation.
Compress attachments
Shrinking file size often provides enough headroom:
- Convert videos to lower resolution or more efficient codecs
- Compress images before attaching (JPEG quality reduction, PNG optimization)
- Use ZIP or RAR compression (particularly effective for documents and spreadsheets)
Compression works best for text-heavy files (documents often compress 50-80%). Media files like JPEGs and MP4s are already compressed — additional compression yields minimal gains.
Use cloud storage
The most reliable solution — attachments become links that consume almost zero email size:
- Upload files to Google Drive, OneDrive, or Dropbox
- Generate a shareable link
- Paste the link in your email body
- Set appropriate access permissions (viewer, editor)
Cloud links bypass server limits entirely (the recipient downloads directly from cloud storage, not through email).
Split into multiple emails
When cloud storage isn’t practical:
- Divide attachments across separate emails
- Number each email clearly (“Part 1 of 3”)
- Ensure each part stays well under the limit (leave margin for encoding)
Reduce HTML complexity
For recurring size issues:
- Strip unnecessary formatting
- Use plain text when design isn’t essential
- Simplify email signatures (remove embedded images, use linked images instead)
Administrator fixes (Exchange)
If you manage the mail server, you can adjust limits:
Exchange Online
Navigate to Exchange Admin Center → Mail flow → Message size limits. Increase the maximum send and receive size (up to 150 MB in Microsoft 365).
Exchange On-Premises
Adjust receive connector and send connector limits in Exchange Management Shell:
powershell
Set-ReceiveConnector “Connector Name” -MaxMessageSize 50MB
Multiple components enforce limits — transport rules, connectors, and mailbox settings all need alignment.
How do you prevent the 552 5.2.3 error?
Avoiding size-related bounces requires workflow changes for routine large-file sharing.
Default to cloud sharing
Make cloud links the standard rather than the exception:
- Integrate Google Drive or OneDrive into your email workflow
- Use the “Insert from Drive” feature in Gmail/Outlook
- Share folders rather than individual files for ongoing collaboration
Compress before attaching
Build compression into your habit:
- Right-click → Send to → Compressed folder (Windows)
- Control-click → Compress (macOS)
- Use batch compression tools for multiple files
Check size before sending
Most email clients display attachment size. Quick mental math: multiply raw size by 1.37 to estimate encoded size. Stay under 80% of the limit for safety margin.
Still stuck after trying the fix?
Some email errors are easy to clear. Others point to deeper deliverability issues involving authentication, sender reputation, blacklisting, routing, or mailbox provider policy. If you would rather have an expert review it, speak with an email delieverability consultant for free and we can help diagnose the issue and fix it on your behalf.
We look beyond the error message itself to find what is actually breaking delivery, trust, or inbox placement.
From SPF, DKIM, and DMARC to blacklist cleanup, DNS alignment, and sending setup, we can guide or implement the fix.
We assess whether the error is part of a bigger pattern hurting opens, replies, and overall campaign performance.
Talk to a real deliverability expert, get honest guidance, and see the next best step without pressure or upsells.
When should you book a consultation? If the error keeps coming back, affects multiple mailboxes or domains, started after an ESP or DNS change, or is tied to spam placement, low inboxing, high bounce rates, or authentication failures, it is usually faster to get an expert involved early.
Frequently asked questions
Here are some commonly asked questions about this error:
Base64 encoding inflates attachment size by approximately 37%. A 24 MB file becomes roughly 33 MB after encoding, exceeding the 25 MB limit. Account for encoding overhead when estimating whether attachments will fit.
Possibly. Microsoft 365 admins can raise limits up to 150 MB. Traditional Exchange deployments allow even higher limits (with performance tradeoffs). Free email providers (Gmail, Outlook.com) have fixed limits that users cannot change.
No. 552 5.2.2 means the mailbox is full (recipient’s overall storage exhausted). 552 5.2.3 means the individual message is too large. Both are size-related, but the causes and fixes differ.
