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How to Fix Exchange Online Error 554-5.3.4 Content Conversion Limit Exceeded
Question details
The user needs to resolve an email delivery failure where Exchange Online rejects a message with error 554-5.3.4 due to exceeding the maximum number of body parts.
- Product
- Exchange Online
- Device & OS
- not provided
- Scenario
- Sending an email that contains complex HTML formatting, multiple embedded objects, or deeply nested email threads.
- Observed behavior
- The cloud mailbox rejects the message, returning error code 554-5.3.4 (Content Conversion Limit Exceeded), typically stating a limit of 250 body parts has been reached.
Check if your email contains an unusually long thread of forwarded messages, numerous embedded images, or excessively complex HTML formatting.
Simplify the Email Message Content
Reduce the structural complexity of your email to bypass the 250 body parts limit.
Exchange Online strictly limits the complexity of an email to protect server performance. Complex tables, lengthy reply chains, and multiple inline images all count toward this body part limit.
Highlight the text in your email body and use the 'Clear Formatting' button to remove complex HTML backgrounds, custom fonts, and intricate tables.
Remove inline images, embedded charts, and interactive objects from the email body. Instead, attach these items as standard file attachments.
Delete lengthy previous email threads and overly complex animated or image-heavy signatures before clicking Send.
Verify Administrator Settings
Work with your Microsoft 365 admin to review organization-wide message delivery restrictions.
Contact Microsoft Support
If simplifying the message and checking admin settings do not resolve the issue, escalate to Microsoft.
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Frequently Asked Questions
What does 'Content Conversion Limit Exceeded' mean?
This error means your email message contains too many distinct structural elements (such as embedded images, deeply nested HTML tags, or attachments). Exchange Online has a hard limit, often 250 body parts, to protect server performance.
Can the 250 body parts limit be increased in Exchange Online?
No, the maximum number of body parts is a hard-coded limit in Exchange Online to prevent resource exhaustion and cannot be manually increased by Microsoft 365 administrators.
Why am I getting error 554-5.3.4 when I have no file attachments?
Even without standard file attachments, an email can exceed the limit if it contains a very long chain of forwarded replies, numerous inline signature images, or highly complex HTML formatting generated by certain email clients.
