Thank you Tarun_Jaiswal.
Typically I convert Excel files to SPSS, then from SPSS to DBF, and then add data as a DBF file. I just tried adding an Excel file directly without having to convert to DBF and it seems to work.
I've only worked with files which have had no more than about 10,000 addresses, so I'm trying to find an efficient way to run 13 million addresses.
I've been told I should put them in a geodatabase folder, but
a. I don't really know what that is,
b. how to get addresses into one, presumably from Excel, or
c. how to geocode them once they are in one,
d. I presume exporting the attribute table with my x,y is the same as what I have been doing.
Merlin