What does 552 mean?

You hit send, and instead of a delivery confirmation, you get back a 552 error. It's not a mystery. It's the receiving server telling you one of two things: your message is too big, or the recipient's mailbox is full.

A 552 is a permanent 5xx failure, which means the server isn't asking you to try again later. It's rejecting the message outright. You'll typically see message text like "552 Message size exceeds limit", "552 Mailbox full", or "552 Message too big".

The two root causes behave differently, so it's worth knowing which one you're dealing with.

Message too large. Every mail server sets a maximum size for incoming messages. If your email crosses that threshold (attachments are usually the culprit), the server won't accept it. The fix is straightforward: strip the attachment and share the file via a cloud link instead (Google Drive or Dropbox work well). Most servers cap incoming messages somewhere between 10MB and 50MB, but the limit varies.

Mailbox quota exceeded. The recipient's inbox is genuinely full. Their storage is maxed out and no new mail can arrive until they clear space. This isn't your fault. If you're seeing this on a business address, it's worth a follow-up through another channel. If it keeps happening to the same address, that's a signal the contact may be inactive or abandoned.

For bulk senders, a 552 due to a full mailbox is worth suppressing after one or two attempts. An inbox that's perpetually full usually belongs to someone who isn't reading email, and continuing to send hurts your sender reputation without any upside.

Still if you're getting 552 errors across many recipients at once, the size limit is almost certainly the cause. Check whether a recent template change added a heavy image or attachment and trim it down.

Seeing a lot of bounce codes and not sure where to start? Our SOS hotline is free, and we're happy to help you read through what your ESP is logging.