BDAT is an extended SMTP (ESMTP) command which is defined in SMTP Service Extensions for Transmission of Large and Binary MIME Messages. It states:
A new SMTP verb, BDAT, is defined as an alternative to the "DATA" command of [RFC821]. When a sender-SMTP wishes to send (using the MAIL command) a large message using the CHUNKING extension, it first issues the EHLO command to the receiver-SMTP. If the receiver-SMTP responds with code 250 to the EHLO command and the response includes the EHLO keyword value CHUNKING, then the receiver-SMTP is indicating that it supports the BDAT command and will accept the sending of messages in chunks.
All IMSVA versions do not support BDAT command. All SMTP clients should not have any problem sending mails to IMSVA without BDAT support.
Unlike DATA command, BDAT command is optional and is only used when both SMTP client and SMTP server support CHUNKING extension.