Mail to Team Cannel - Remote Server returned '554 5.4.0'

[MySergius]

Hi
I have a strange effect with sending Mail to a Teams Channel. If send an external User user1@domain.com a mail to the Teams channel, the recive a NDR with the following text
Remote Server returned '554 5.4.0 < #5.4.182 smtp;554 5.4.182 Problem occurred during the delivery. Exception Message:The remote server returned an error: (400) Bad Request.>'

If an other external user from the same Company user2@domain.com send a Mail will delivered to the teams Channel.

[#2]

@MySergius Do you still have the same problem? And if so do you have the same problem when you send to different channels? My guess is that there were some temporary problem in the mail relay handling emails to Teams channels.

[#3]

Hi @Linus Cansby 

I have still the problem. We testet with a different channels with the same resultant.  

[#4]

Hello@MySergius 

is your problem resolved? and how ?

I have the same error message when I redirect an external mail to a Teams channel (via the automatic exchange mail redirect)

Remote Server returned '554 5.4.182 Problem occurred during the delivery. Exception Message:The remote server returned an error: (400) Bad Request.'

[#5]

@Microsoft ?!?! @support  @Microsoftsupport @Support @supportKO @mssupport

When answer resolve this problem??!?!!?

[#6]

@MySergius We're experiencing the same issue. I've rebuild my scripts so that SendGrid is used for mail distribution but that also ends up with the error 400. Main issue is that the 'sending ip' appears to be not responsive for that domain. It suggests it has something to do with SPF.