The 554 5.7.0 “illegal attachment” error means the receiving server blocked your email because it contains a prohibited file type — typically executables (.exe), scripts, or archives containing dangerous content.
Fix it by removing blocked attachments, uploading files to cloud storage (Google Drive, OneDrive, Dropbox) and sharing links instead, or repackaging content in accepted formats.
Security-conscious organizations block attachment types commonly used for malware distribution.
The rejection protects recipients from potential threats — but also catches legitimate business files. Understanding what’s blocked (and why) helps you deliver content through alternative means.
Quick skim — 554 5.7.0 error overview
The 554 5.7.0 error indicates a security policy rejection based on the attachment’s content.
| Attribute | Details |
| Error code | 554 5.7.0 |
| Category | Security policy / content rejection |
| Meaning | Attachment type violates the recipient’s security policy |
| Severity | Permanent (requires attachment removal or format change) |
| Common causes | Blocked file types, nested archives, macro-enabled files |
| Fix approach | Remove attachment → use cloud links → verify authentication |
What does illegal attachment mean?
Mail servers and security gateways maintain lists of blocked file types. Messages containing these attachments receive automatic rejection — regardless of actual content safety.
Commonly blocked file types
Most organizations block executable and script files:
- .exe, .com, .bat, .cmd — Windows executables
- .scr, .pif — Screen savers and program information files
- .dll, .ocx — Dynamic libraries
- .vbs, .js, .ps1 — Script files
- .msi, .msp — Installer packages
- .hta — HTML applications
Macro-enabled documents
Microsoft Office files with macros face increasing scrutiny:
- .xlsb — Binary Excel workbooks
- .docm, .xlsm, .pptm — Macro-enabled Office files
- Password-protected ZIPs containing Office files (can’t be scanned)
Archive concerns
Archives receive special attention because they can hide blocked content:
- Nested archives (.zip inside .zip)
- Archives containing any blocked file type
- Password-protected archives (contents can’t be scanned)
Why does the 554 5.7.0 error occur?
Attachment blocking stems from security policies enforced at the receiving organization.
Blocked file extension
The receiving server’s policy prohibits specific extensions regardless of file content. A legitimate business application (.exe) triggers the same block as malware.
Nested compression
Zipping a ZIP file creates a structure that triggers security flags:
- Can’t scan the inner archive contents efficiently
- Common malware distribution technique
- Often blocked outright by policy
Aggressive security policy
Organizations in regulated industries (finance, healthcare, government) often implement strict policies that block:
- All archives
- All Office files with macros
- Files from unknown senders
- All executables (no exceptions)
Content scanning failure
Some security gateways block attachments they can’t scan:
- Encrypted files
- Corrupted archive structures
- Unusual compression formats
- Files exceeding scan size limits
How do you fix illegal attachment detected?
Working around attachment blocks requires alternative delivery methods.
Use cloud storage
The most reliable solution — bypass attachment restrictions entirely:
- Upload file to Google Drive, OneDrive, or Dropbox
- Generate a shareable link
- Set appropriate permissions (view, download, edit)
- Send the link in your email body
Cloud links work regardless of recipient security policies (though some organizations block cloud storage domains).
Remove blocked attachments
If the attachment isn’t essential:
- Delete the attachment
- Describe the file contents in the email body
- Offer to share via alternate means upon request
Repackage content
Convert blocked formats to accepted alternatives:
- PDF exports instead of macro-enabled Office files
- Documentation instead of scripts (recipient can recreate)
- Screenshots instead of executables (for UI demonstration)
Rename file extensions
Sometimes works (use cautiously and only for legitimate files):
- Rename .exe to .ex_ with instructions to rename back
- Add .txt extension to script files
- Recipient renames after download
Many security systems examine file headers (not just extensions), so renaming doesn’t always bypass scanning.
Verify authentication
Some 554 5.7.0 errors aren’t actually about attachments — authentication failure can produce the same code:
- Verify DKIM signatures are valid
- Confirm DMARC alignment passes
- Check SPF records to authorize your sending IP
Run an email deliverability test to verify authentication status.
Check blacklist status
Sender reputation problems can trigger 554 5.7.0 alongside (or instead of) attachment issues:
- Verify IP isn’t blacklisted
- Check domain reputation
- Request delisting if necessary
Contact recipient
When legitimate business needs require sending blocked file types:
- Ask the recipient to whitelist your address
- Request temporary policy exception
- Coordinate an alternative delivery method
How do you prevent this error?
Understanding recipient policies and defaulting to safe delivery methods prevents attachment rejections.
Default to cloud sharing
For any file over 5 MB or any potentially blocked type:
- Use cloud storage links automatically
- Mention the file type in the email body for context
- Set permissions before sending
Know common blocks
Before sending unusual attachments:
- Expect script files to fail
- Consider macro-enabled Office files risky
- Assume executables will be blocked everywhere
Compress thoughtfully
When using archives:
- Single-level compression only (no nested zips)
- Don’t password-protect unless the recipient expects it
- Use standard ZIP format (avoid exotic compression)
Maintain sender reputation
Strong authentication reduces the likelihood of reputation-based 554 errors:
- Configure SPF, DKIM, and DMARC properly
- Monitor email deliverability regularly
- Address blacklisting promptly
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:
Not typically. Attachment policies are set by the recipient’s organization — they won’t change policy for individual senders. Use cloud sharing as a reliable alternative.
Security policies often block all archives (or archives containing certain types) because archives can hide malicious content. Additionally, nested archives (.zip inside .zip) trigger additional flags regardless of contents.
No. The 5.7.0 code indicates “other or undefined security status” — attachments are one cause, but authentication failures and sender reputation can also trigger this generic security rejection. If removing attachments doesn’t help, investigate SPF/DKIM/DMARC and blacklist status.
