Generic SMTP
552 5.3.4 Message too large — reduce the email size
552 5.3.4
The message was larger than a mail system could accept. The limit may belong to your outbound service, the recipient's gateway, the destination mailbox provider, or an intermediate security system. Attachments expand during email encoding, so a file below a published limit can still produce a message above it.
How to fix it
- 1
Remove or compress attachments
Delete unnecessary files, compress suitable documents, and resize large images. Remember that email encoding adds overhead beyond the original file size.
- 2
Share large files with a controlled link
Put the file in an approved storage service and send an access-controlled link instead of attaching it.
- 3
Check both sides' limits
Compare the sending service, outbound gateway, recipient gateway, and mailbox-provider limits. The smallest enforced limit wins.
- 4
Resend only after the message changes
This is a 5-class permanent result for the oversized message. Queue retries of the same bytes will not make it fit.
Meaning current as of 2026-07-15, cross-checked against the provider's own documentation. Providers do occasionally redefine codes — if this doesn't match what you're seeing, the source link is the authoritative reference.