554: message too large
Your message is larger than the recipient company’s size limit in Mimecast, or larger than Mimecast’s own limit, so it was refused.
- Mimecast
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 554
- Provider
- Mimecast
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
554 Maximum email size exceeded.
What it means
Mimecast rejects messages over the size set by a customer’s Email Size Limit policy or over the service’s own limit, by default 100 MB on its legacy MTA and 200 MB on its latest one. The size that counts is the encoded message as it travels, which is larger than the files attached: Mimecast notes that a 70 MB attachment can push a message past 100 MB. The rejection is permanent and the message must be sent again in a smaller form. A company’s own limit can be much lower than Mimecast’s.
Common causes
- Large attachments, whose encoding adds roughly a third to their size.
- A size limit set by the recipient company that is lower than your attachment.
- Several attachments or embedded images adding up.
How to fix it
- 01Send the file as a link to a file sharing service instead of an attachment.
- 02Compress or split the attachment and send it in parts.
- 03Ask the recipient what size limit applies if you need to send large files often.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Policies - Mimecast SMTP Error Codes (Mimecast support)mimecastsupport.zendesk.com
Related codes
554 at other providers
- 554Permanent rejection (554).Yahoo or AOL rejected the message for good with a 554. Yahoo uses this code for several problems, from failed authentication to unacceptable content, so the wording of the reply tells you which.
- 554Failed authentication.Yahoo or AOL refused the message because it failed the checks that confirm the sending domain, such as DKIM against the domain's policy. Yahoo lists this among its permanent 553 and 554 errors.
- 554Recipient does not exist.The Yahoo or AOL account you wrote to does not exist. The failure is permanent: check the address with the recipient, and remove it from any list.
- 554No reverse DNS (PTR) record.Xfinity refused the connection because your sending IP has no PTR record. Every server sending to Xfinity needs valid reverse DNS, so the owner of the IP must add one.
- 554Rejected for breaking GMX guidelines.GMX refused the message permanently because the connection broke its guidelines. GMX points to its requirements page and asks for the full error message if the problem continues.
- 554IP address on the GMX blocklist.Your sending IP is on a blocklist that GMX manages itself, so its servers refuse the connection. GMX keeps a strict no tolerance policy toward spam.
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