Run several instances of grep. Instead of
grep -i user@domain.com 1US* | awk '{...}' | xargs rm
do
(for i in 1US*; do grep -li user@domain "$i"; done) | xargs rm
Note the -l flag, since we only want the file name of the match. This will both speed up grep (terminate on first match) and makes your awk script unrequired. This could be improved by checking the return status of grep and calling rm, not using xargs (xargs is very fragile, IMO). I'll give you the better version if you ask.
Hope it helps.
