The Dublin Evening Mail offices were in what were, I think, later on to become the Dublin Corporation Rates Office, when the Mail closed forever sometime in the 1950's, - This is a rather nice building just beyond the upper gate of the Castle on the other side of the street.
I seem to recall a connection between the Evening Mail and the Irish Times. Could this have also been the Express office?
Thoms is your man.
By the way it is by no means infallible.