Second email address not visible in Signature drop down menu?

[AlwaysDNS]

Hi All..

 

Got a strange issue with a user who has read\manage\send access to a licenced user mailbox that's used as a shared mailbox for the admin team.

 

On their first day starting we manually added the inbox to their Outlook 2019 client via the usual account settings route and they were able to set a different signature for the mailbox (Signature, New signature, selected the second mailbox from the drop down menu).

 

Now the user switches between 3 or 4 PC's - on her first login to these machines the mailbox has auto-deployed to the client (fab)... but when trying to setup the signature it's not in the selectable email address drop down in the signature menu.

 

Even though the mailbox has deployed to these 3/4 PC's - I've added the second mailbox via account settings but it still doesn't appear in the signature drop down.

 

So at the moment, apart from the PC they were on the day they started they don't have an email signature for the second mailbox.

 

Any ideas?.. I know it could be set in OWA no doubt, but need I need to stick the client.

 

Thanks in Advance!

ADNS