Users of Exchange Online or Exchange Online Protection may not receive an expected email message. If you perform a trace on the message, you find that message delivery failed and that a nondelivery report (NDR) that contains the following error message was generated:
Users may not have experienced this problem in the past when they used Forefront Online Protection for Exchange (FOPE).
SMTPSEND.BareLinefeedsAreIllegal; message contains bare linefeeds, which cannot be sent via DATA
This issue occurs if the source message transfer agent (MTA) didn't append the expected CR-LF combination to the end of the message as documented in Request For Comments (RFC) 2822.
To resolve this issue, do one of the following, as appropriate for your situation:
- Request that the sender correct the message format. This error frequently occurs with automated mailers (for example, reports or invoices) and bulk senders.
- Enable Extended SMTP (ESMTP) on the receiving server so that the message can be sent by using CHUNKING or the BDAT command. Neither of these methods depends on the CR-LF combination to signal the end of the message. For more information, see SMTP protocol extensions.
- If the sender cannot correct the sent messages, or if the gap must be bridged until the message format is corrected, the recipient can create an inbound transport rule to append a disclaimer to the messages from the problematic sender. The disclaimer will append the expected CR-LF combination to the message so that it can be delivered. (This disclaimer may consist of a single character such as a period or a dash.)