agent is assigned a ticket and logs into OSticket to send a reply to the user.
When the user replies, agent recieves an email in his external mail system wth the message
agent is short of time so instead of logging into Osticket to reply he replies direclty to the notification email. His reply can be seen in osticket against the ticket - but the user does not get a reply email.

Is this correct or should it work like this?

ntozier Thanks.
That is a shame, so users can use external email to contact agents, but agents MUST log in and use the OSticket inteface

As long as we know that is fine. But I bet I get some grumbling ?

There some threads (both here and at github) where people have figured out how to change this behavior, but they were for older versions (ie not 1.12) so if you know PHP you might be able to figure out how to change it and could mod your instance.

I would like to see a toggle in the admin settings of osTicket to decide how to handle Agent email responses personally, but it hasn't happened you.