431 DNS temporary failure at return MX check,

[Guest]

....try again later (#4.3.0)

We've been receiving this error message from Outlook "Unable to send
...." and the rest of it in my subject, for the last hour. Can somebody
let me know what the problem is?

TIA
Russel

 

[Vince Averello [MVP-Outlook]]

Sounds like a potential issue with your SMTP server or something upstream
from it. Have you contacted your Internet provider or internal IT staff?

 

[Guest]

Thanks, Vince. You caught it in one. I wrote to our Internet provider
and they will help. Apparently this is caused by something called a
returnMXcheck which needs to authenticate the sender on the ISP's server
and they'd neglected to authenticate us :-(

Thanks and regards,
Russel