Documentation
5.3.4: the message is too large for the receiving server.
Your message is bigger than the limit the recipient's server allows.
What it means
Every mail server sets a maximum message size. When a message is over it, the server answers 5.3.4 (message too big for system) or 5.2.3 (message length exceeds administrative limit). The size that counts is the encoded message, and attachments grow by about a third when they are encoded for email, so a 15 MB file becomes a message of roughly 20 MB.
Typical codes and wording
552 5.3.4, 5.2.3 ("message too large", "exceeds size limit")
Common causes
- A large attachment, or several attachments that add up.
- Inline images that were embedded at full resolution.
- A recipient whose server has a lower limit than yours.
What to do
- Shrink or remove attachments, or compress images before embedding them.
- Link to a hosted file instead of attaching it, which also avoids the receiver's limit entirely.
- Keep messages well under the limits of the places you send to: many providers stop at around 20 to 25 MB.
- There are limits on this side too: the delivery network accepts an encoded message of up to 40 MB, and the SMTP relay accepts up to 18 MB, attachments included.
What Mailtruss shows
Titled "Message is too large for the receiving server". It is a permanent bounce for that message, so the address is added to your suppression list; the address itself was fine, so remove it again once you have a smaller message to send.
Is it safe to retry?
Only after you make the message smaller.