Email does not get through

Product is "Email Advanced"

Please open a support ticket.

Hello Chriz,

Thank you for reaching out to the community, This happens because the forwarded email contains the original sender's HEADER FROM. Since Sophos Central Email is a SaaS solution and it is shared by many tenants, it needs to have a way to determine which emails are for your organization. The way it does this is by using the HEADER FROM email address. If the domain here is not one of your configured domains AND the email address is not a MAILBOX on your Central account, you will get a reject message. You should look into other options such as bypassing Central Email for auto forwarded emails or doing some HEADER FROM rewriting.

What exactly should I write to the supplier now? He gets this error when he sends us an email! Is it him or us (sophos).

Chriz, are you sure the recipient has a valid mailbox in your organization? The sender is sending to user@yourcompany.com there must be a valid mailbox configured in Central for user@yourcompany.com or an alias of an existing mailbox. If not it will be rejected. If there is a valid mailbox the message should be accepted and then inspected for spam, malicious content etc

If you are certain there is a valid mailbox please log a support ticket so we investigate further.

I copied the recipient address from the error message and sent email myself. This works. Support has everything I have.

ok thanks for confirming and as Vivek noted if this the results of an forward where it doesn't change the from header it will be blocked as a relay attempt. 

But surely it must be possible for a customer or supplier to forward an email? I do not understand it.

Yes IF you or I forward an email from our client it changes the FROM to yours or my email address. If an auto-forward is not setup correctly it leaves the original authors email address which doesn't have permission to send email through Sophos. That would create an open relay and we don't allow that.  Look through this forum posts for some others which explains it further and how to handle it at the server level - https://community.sophos.com/sophos-email/f/discussions/135767/forwarding-email-from-exchange-2019-not-working

Hello,

the sender just informed me that this is a new email and not a forwarded one.