Usually the bounced back email message says a bit more; offering some info on possible cause.

Can you tell us the full error message .... word for word or post an image ?

Maggie007 said

I've recently started using Thunderbird (in windows 10). I have problems sending messages to some e-mail adresses, it seems mostly business adresses, to e.g. sending to gmail adresses is no problem. Right away I get a delivery status notification failure, which says action: failed status: 5.4.0 Would be grateful if anyone knows what the problem might be.

This is the full error message:

This is an automatically generated Delivery Status Notification.

Delivery to the following recipients failed.

     e-mail address

Reporting-MTA: dns;cpsmtpb-ews01.kpnxchange.com Received-From-MTA: dns;cpsps-ews18.kpnxchange.com Arrival-Date: Sat, 2 Sep 2017 09:20:22 +0200

Final-Recipient: rfc822;e-mail address Action: failed Status: 5.4.0

The error code says: 5.4.0 DNS Problem. Check the Smart host, or check your DNS. It means that there is no DNS server that can resolve this email address. Could be Virtual Server SMTP address.

Check that you typed the recipients email address correctly, particularly the domain part.

If I send exactly the same message to the same e-mail address from webmail, there is no problem at all. The recipients email adresses are correct, this is not the problem.

Then you should talk to your email provider.