552 5.3.4: the message is too big

552 5.3.4 is a permanent SMTP reply: message too big. This page is part of our SMTP error code reference, where every code links to the RFC and to what Gmail, Outlook and Yahoo publish about it.

Kind

Permanent: sending the same message again fails the same way

Retry by hand

No, fix the cause first

In Mailbay

bounced, address not suppressed

What 552 5.3.4 means#

552 is "Requested mail action aborted: exceeded storage allocation" ^[1]. X.3.4 is "Message too big for system": "The message is larger than per-message size limit", and it is "useful only as a permanent error" ^[2].

Servers that support the SIZE extension announce their limit in the EHLO answer, such as SIZE 26214400 (25 MiB). A client that declares a larger size in MAIL FROM is refused before it sends any data.

What Gmail, Outlook and Yahoo say#

Gmail

"552 5.3.4 Your message exceeded Google's message size limits." Other 552 5.3.4 rows cover too many attachments and headers that are too large ^[3].

Outlook and Microsoft 365 and Yahoo do not list 552 5.3.4 on the error pages we read, so we do not guess what they mean by it.

Common causes#

• Large attachments. Base64 encoding makes each attachment about a third larger than the file.
• Images embedded in the HTML instead of linked.
• Many recipients' servers have lower limits than yours.

How to fix it#

1. Send large files as links to storage instead of attachments.
2. Compress or resize images before attaching them.
3. Do the arithmetic with the encoded size: a 20 MB file is close to 27 MB once encoded.

How Mailbay reports it#

When a recipient's server answers 552 5.3.4 to mail you send through Mailbay, the recipient becomes bounced and you get a message.bounced event with the server's reply in response and permanent: false. The message statuses page lists every state.

A policy refusal says nothing about whether the address exists, so Mailbay does not suppress it, and it does not count toward the automatic pause, which only counts hard bounces and spam complaints.

Mailbay's receiving and submission servers announce SIZE 26214400 and answer 552 5.3.4 Message size exceeds fixed maximum message size above it. The API refuses a send over 25 MB after encoding before anything is sent (sending limits).

Related codes#

• 550 5.1.1: mailbox does not exist, permanent.
• 421 4.7.0: temporary refusal, connection closed, temporary.
• 530 5.7.0: sign in first, permanent.
• 451 4.7.1: deferred: rate limit or policy, temporary.
• 550 5.7.1: refused for a policy reason, permanent.

Seeing an API error rather than an SMTP code? Mailbay's own errors, each with a fix, are on the errors page.