SMTR-749 — SMTP command argument parsing error
The smtp-proxy parses client commands up to the RCPT one, but found errors (see smtp-error enumeration description in mod-mail-doc(5) manual page) are only collected to a set of flags. For every recipient, the flags are used to help choosing a proper DELIVERY-ACL (that can but need not to use these flags). If the result of the delivery-acl is negative (i.e. ABORT, REJECT, REFUSE, DISCARD or block by grey-listing) and some error in argument parsing has occured, this messages is logged to facilitate the admin to find the reason for delivery-acl decision (if the flags were used). Of course, if the chosen acl does not contain any criteria concerning the command argument flags, this message is not relevant.
Check the SMTR-802 message for the name of chosen delivery-acl and action taken. If the acl works with command argument flags, you can find the flags (%2 and %5) in this log message. If the value %1 or %4 is "INVALID", it means that particular command argument was not correct and preceding error log messages should be checked, too.