[ms office - o365] Exchange 365 - external recipients can't see previous email thread

[Network_Boy]

Our users are having a problem where when they forward/reply an email thread to an external email recipient, the recipient can't see the previous thread - only the body of the email they have just been sent. When the same email thread is forwarded to an internal recipient, they can see the previous thread just fine.

 

I have tested this myself and when I check my sent items, those emails sent to external recipients DO NOT show the previous email thread, whereas those sent to internal recipients do. When you are composing the email, the thread shows and looks as though it will be sent.

 

This behaviour is the same whether sent from Outlook desktop or OWA. The settings in local Outlook itself look fine, in that if you go to File > Options > Mail > Replies and forwards - the settings in here are set to "Include original message text". Which is leading me to think it might be a setting in Exchange/Security Admin Center.

 

Is anyone having the same issue / know the fix? TIA.

[Network_Boy]

We now have this working properly again. Turns out the cause was our CodeTwo software, which we use for our email signatures. Some of the HTML was commented out, and it didn't like that. Hopefully this will help someone out!