Exchange 2007 "reply" emails being bounced

[worcestertech]

Hi everyone.

 

This issue started happening around mid day yesterday.

 

Exchange 2007, outlook clients (2007 - 2013)

 

We can send and receive emails OK with one big exception; anyone outside our organization who replies to an email gets bounced with a "571: Delivery not authorized" message.

 

An external sender can send us a new email absolutely fine but if the same person replies to one of ours it's bounced.

 

Nothing (that I know of) has been changed at this end and until yesterday there were no problems.

 

I'm not coming up with any conclusive answers, does anyone have any ideas? I could do with a very quick fix here.

[howartp]

Do you have one domain, or more than one?

 

Are your outgoing emails correctly going from the email address you expect, or are they going out from a domain you only use internally (for example)?

 

Thus when they write a new email to you, they address it to [email protected], but when you send an email out it goes from [email protected] so when they reply, the reply tries to go to [email protected] which is configured to only allow internal emails?

 

Peter

[worcestertech]

***Update***

 

Denial is being carried out by the spamblocker service on our WatchGuard XTM505. As a temporary measure I've changed the proxy action to add a label rather than block the message.

 

However, this begs the question: why would WatchGuard suddenly start to see any replies to our emails as "confirmed spam"? I've made no changes either to Exchange or WatchGuard. I can't see anything in the mail headers that's untoward.

 

Does anyone have any idea what I could / should be looking for?

[worcestertech]

Hi Howartp, our posts crossed.

 

As you can see it's not an exchange issue, well not directly anyway. I can see no anomalies in the reply-to or any other part of the header but WatchGuard insists that any reply is spam so there must be something that I'm missing.