Start with the full rejection, not the attachment size
A 5.3.4 size refusal means the complete email exceeded a per-message limit at the system that rejected it. Read the full delivery-status notice to identify that system before changing your hosting account. A 552 reply can accompany different problems; 5.2.2 points to a full recipient mailbox, while 5.3.4 identifies a message too big for the mail system.
This guide applies when a Novasean-hosted mailbox or VPS mail service is part of your accepted service, or when a message from it is rejected by another provider. It does not establish a Novasean-wide message-size limit or permission to change one. If the bounce names an external recipient server, its operator controls that receiving policy.
Find the rejecting hop in the bounce
- Keep the complete SMTP reply and enhanced code, the rejecting hostname, affected recipient and time with time zone. Preserve the message ID if present. Redact private addresses and message content before sharing the notice with support.
- Find whether your mail client was refused during initial submission, your outgoing server accepted the message and later returned a bounce, or the remote recipient provider rejected it. A copy in Sent does not prove the next server accepted delivery.
- If the recipient agrees to a test, send one small, harmless message to that address; otherwise use an address you control on the same receiving service if available, or skip this comparison. A successful small message alongside a
5.3.4rejection of the larger one supports a size diagnosis only when both messages follow the same route. If both fail, use the exact smaller-message error rather than assuming a size limit.
Do not raise a DirectAdmin mailbox-storage quota because a remote system rejected the size of a single message. The mailbox-full guide covers the different 5.2.2 condition.
Why a file below the advertised limit can still fail
An SMTP limit applies to the transmitted message, not just the files shown in the attachment picker. The message includes headers, body, MIME boundaries, inline images and encoded attachments. MIME base64 turns each three input octets into four output characters; for example, a 12 MiB binary file needs at least 16 MiB of base64 characters before line breaks and the rest of the email. Forwarded threads and signatures add more.
The SMTP SIZE extension can advertise a maximum and let a sender declare an estimated message size before transfer. A server may reject at that point or after it receives the message; another server later in the route can apply a lower limit. Do not treat a mail client's displayed file size or one provider's published cap as the effective end-to-end limit.
Reduce the message or agree a safer transfer route
Remove unneeded attachments and quoted history, or produce a smaller approved version of the file without discarding information the recipient needs. Send a fresh message to the original recipient and check its result. If the material must remain intact, agree an access-controlled file-sharing or transfer route with the recipient; check permissions, expiry, retention and confidentiality before sending a link. A link can still be blocked by the recipient organisation, so confirm its accepted method.
Repeatedly resending the same oversized attachment cannot change a fixed limit. Splitting a sensitive file into several emails can create incomplete copies and bypass a recipient's intended policy; agree the method with the recipient instead. Avoid uploading customer data to an unapproved third-party service merely to get under an email limit.
Ask the operator of the rejecting server about its limit
If a confirmed Novasean-operated outgoing server rejected the message, give support the redacted reply, message size shown by the client if available, timestamp and service identity. Ask for the effective submission policy and the supported alternative. Exim has an operator-level message_size_limit, but a server-setting change can affect resources and does not override a later recipient limit. A customer should not edit Exim configuration or assume a limit increase is included in their service.
For a self-managed VPS, the authorised administrator can inspect the mail service's own configuration and logs under their change control. For a managed service, server-level investigation belongs to its operator. If the remote recipient provider rejected the message, its operator must explain or change that policy; Novasean cannot enlarge a third party's receiving limit.
Verify the new message reached its intended recipient
After reducing the message or agreeing a transfer route, send a fresh controlled message. Confirm the sender received no new bounce and ask the recipient to confirm the actual message or file is accessible. A successful SMTP submission alone is not proof of recipient delivery. Keep the final message ID and redacted outcome for support if the problem persists.
If the next reply is 5.2.2, follow the mailbox-full guide; if it is a connection or authentication error, follow the receive-but-cannot-send guide. Resolve the code you now have rather than continuing to adjust attachment size.
Common questions
Does every 552 mean my attachment is too large? No. Read the enhanced code and words; 5.2.2 is a mailbox-full condition, while 5.3.4 identifies a per-message system limit.
Can I increase my DirectAdmin mailbox quota to fix 5.3.4? Not as a general fix. Mailbox storage and maximum message size are different controls, and a remote server may be the one refusing the message.
Why did a smaller file send? The complete encoded email may have fallen below the rejecting system's limit. That comparison supports a size diagnosis but does not establish an exact account-wide threshold.
Will the original bounced message retry by itself? Do not rely on automatic delivery after a permanent refusal. Send a new message by the approved route and confirm receipt.
Sources and technical references
Related guides
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