552 5.3.4 Message size exceeds fixed limit Email / SMTP Origin: Network Last updated 4 Nov 2026

SMTP: 552 5.3.4 Message size exceeds fixed maximum message size

The message, including attachments after base64 encoding, is larger than the receiving or sending server accepts.

Exact message you may see 552 5.3.4 Message size exceeds fixed maximum message size552 Message size exceeds fixed limit552-5.2.3 Your message exceeded Google's message size limitsmessage file too big552 5.3.4 Message too big for system
Explore the map of this error Full error map →
Seen on: SMTP

Meaning

Attachments grow about 33 percent when encoded, so a 20 MB file becomes ~27 MB. Gmail accepts 25 MB, many hosts 10-20 MB. Fix by sharing a link instead, compressing the file, or raising message_size_limit on your own server (and the proxy/webmail in front of it).

Common causes

  • Large attachments (base64 overhead included)
  • Receiving server limit lower than yours
  • Your own Postfix/Exim message_size_limit too low
  • PHP/WordPress upload limits when sent from a form
  • Recipient quota nearly full

⚡ Quick fix

  1. Upload to cloud storage and send a link
  2. Compress the attachment or split it
  3. Raise message_size_limit if you run the server

Detailed fix by platform

Postfix

  1. postconf -e 'message_size_limit = 52428800' then postfix reload; mailbox limit too: postconf -e 'mailbox_size_limit = 0'

How to diagnose

  1. Size — Encoded size vs limit?
  2. Side — Sender or receiver limit?
  3. Server — Own server limit?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: Network. Errors that are often confused with or caused by this one (click to open):

421 4.7.0 Try again later (rate limited) — SMTP: 421 4.7.0 Our system has detected an unusual rate of unsolicited mail originating from your IP address. Mail sent from your IP address has been temporarily rate limited (Email / SMTP)421 4.7.0 Try again l…450 4.7.1 Greylisted, please try again later — SMTP: 450 4.7.1 <user@example.com>: Recipient address rejected: Greylisted, see http://postgrey.schweikert.ch/help/example.com.html (Email / SMTP)450 4.7.1 Greylisted,…451 4.3.0 Local error in processing — SMTP: 451 4.3.0 Error: queue file write error / 451 Requested action aborted: local error in processing (Email / SMTP)451 4.3.0 Local error…452 4.2.2 Mailbox full / over quota — SMTP: 452 4.2.2 The email account that you tried to reach is over quota (Email / SMTP)452 4.2.2 Mailbox ful…452 4.5.3 Too many recipients — SMTP: 452 4.5.3 Your message has too many recipients / 452 Too many recipients received this hour (Email / SMTP)452 4.5.3 Too many re…530 5.7.0 Authentication Required — SMTP: 530 5.7.0 Must issue a STARTTLS command first / 530 5.7.1 Authentication required (Email / SMTP)530 5.7.0 Authenticat…554 5.7.1 Service unavailable; client host rejected — SMTP: 554 5.7.1 Service unavailable; Client host [203.0.113.5] blocked / 554 5.7.1 <mail.example.com>: Client host rejected: Access denied (Email / SMTP)554 5.7.1 Service una…552 5.3.4…

Explore the map of this error Full error map →

🧠 Still stuck? Analyze your error

Paste the full message, response headers or stack trace — we'll detect the platform and point to the most likely cause.

💬 What worked for others

No tips yet — did something else fix this for you?

Share what worked for you

Tips are checked by an editor before they appear. Links are removed.