Solaris

find . -type f -name "copy*" exec grep example.com {} \;

find . -type f -name "copy*" exec sed -e 's/user@example\.com/user2@example\.com' {} \;

find . -type f -name "example*" -print > list.txt
for file in `cat list.txt`; do
  sed -i "s/user@example\.com/user2@example.com/g" $file
done

find . -type f -name "copy*" exec perl -pe 's/user\@example\.com/user\@example.com/' {} \;

find . -type f -name "copy*" -print |
while read file; do
 cp "$file" "$file".tmp &&
 sed 's/user@example\.com/user2@example.com/' "$file".tmp > "$file" &&
 rm "$file".tmp
done

find . -type f -name "example*" -exec ksh -c 'sed "s/user@example.com/user2@example.com/g" "$1" > /tmp/sed.$$.out && mv /tmp/sed.$$.out "$1"' ksh {} \;

for fname in example*; do
    [ -f "$fname" ] || continue
    printf '%s\n' 'g/user@example\.com/s//user2@example.com/g' w q | ed -s "$fname"
done

for fname in example*; do
    [ -f "$fname" ] || continue
    ed -s "$fname" <<-'EOED'
         g/user@example\.com/s//user2@example.com/g
         w
         q
    EOED
done

find ... | while IFS= read -r filename; do ...