CHUNKING
An SMTP extension (RFC 3030) that sends the message in counted chunks with BDAT instead of DATA, so no end-of-data dot or dot-stuffing is needed.
What it means
With CHUNKING the client sends BDAT followed by the exact number of octets in the next chunk, then the octets themselves, and marks the final chunk with BDAT n LAST. Since the server always knows how many octets to read, nothing inside the message can be mistaken for its end, and the BINARYMIME extension, defined in the same RFC, can carry unencoded binary content on top of it.
The two methods must not be mixed in one transaction. Gmail supports BDAT and answers a DATA command sent after BDAT with 503 5.5.1.
Example
C: BDAT 86 LAST
C: (86 octets of message)
S: 250 2.0.0 OKRelated terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 3030: SMTP Service Extensions for Transmission of Large and Binary MIME Messagesrfc-editor.org
- Google Workspace Admin Help: Gmail SMTP errors and codesknowledge.workspace.google.com
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