Use grep to find content in files and move them if they match

If you want to find and move files that do not match your pattern (move files that don’t contain 'Subject \[SPAM\]' in this example) use:

grep -L -Z -r 'Subject: \[SPAM\]' . | xargs -0 -I{} mv {} DIR

The -Z means output with zeros (\0) after the filenames (so spaces are not used as delimeters).

xargs -0

means interpret \0 to be delimiters.

The -L means find files that do not match the pattern. Replace -L with -l if you want to move files that match your pattern.

Then

-I{} mv {} DIR

means replace {} with the filenames, so you get mv filenames DIR.