This document explains the problem: https://docs.microsoft.com/en-us/exchange/mail-flow-best-practices/non-delivery-reports-in-exchange-online/fix-error-code-550-5-6-11-in-exchange-online
I will omit my thought on remote admins. A very simple rule in communication is: be strict when sending, be tolerant when receiving. Regards, Tonino Il 28 agosto 2022 19:24:13 CEST, Jeff Koch <jeffk...@intersessions.com> ha scritto: >Further information: > >The sender also got the following message from his exchange mailserver when >trying to send to our mailserver: > >Your message contains invalid characters (bare line feed characters) which the >email servers at ......com don't support > >Jeff > > >On 8/28/2022 12:45 PM, Jeff Koch wrote: >> >> Never heard of this before but an email sender to our mailserver got the >> following error message: >> >> 550 5.6.11 SMTPSEND.BareLinefeedsAreIllegal; message contains bare >> linefeeds, which cannot be sent via DATA and receiving system does not >> support BDAT >> >> Does anyone know whether the qmail toaster supports the SMTP protocol BDAT >> command ? >> >> Thanks, >> >> Jeff