Messages with empty TO and FROM fields in headers (not in the "message envelope") are rejected by Intermedia spam filters with the following error message:
550 Error: Message content rejected
This is true for inbound mail only.
Such messages are usually the result of inappropriate behavior by the sender (such messages are usually sent by spammers). In rare cases they are produced by incorrectly written scripts or buggy mail clients. They are usually interpreted as "corrupted" and cannot be processed by the majority of mail clients such as Outlook Express, Microsoft Outlook, and so on.
Reference: Empty TO/CC/FROM fields in headers are in violation of the regulations in RFC 2821 (3.8.4 Other Header Fields in Gatewaying).