# SMTP: 552 5.3.4 Message size exceeds fixed maximum message size

**Code:** `552 5.3.4 Message size exceeds fixed limit` · **Category:** Email / SMTP · **Seen on:** SMTP

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

## 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?

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Source: [WhatIsMyError](https://whatismyerror.com/errors/email/552-5-3-4-message-too-large)