1. Rebex SMTP does not send additional BDAT chunks once it receives an error response to one of them. However, a server-side log doesn't show how things look like from the client-side due to communication latency. In this case, the SMTP client used chunking and pipelining (RFC 2920) together, which means it was permitted to send multiple BDAT chunks without waiting for the server response to each of them. And it actually managed to send all the chunks before it received the error response by which the server rejected one of them.
2. Rebex SMTP doesn't provide any retry mechanism of its own. This is outside the scope of Rebex Secure Mail. A robust retry mechanism would have to operate reliably even if the application has terminated and restarted, which means some kind of permanent storage for outgoing messages would be needed, and it's not a responsibility of a SMTP client library to provide that.
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