Ram, I think OP wants to align each of the 800+ FASTA files individually and write the corresponding output. So, there will be 800+ output files. Assuming OP has the FASTA files with .fasta extension, the following script will run MAFFT and write output with suffix .out added to the input file name.
for fasta_file in $(ls *.fasta)
do
mafft --retree 1 $fasta_file > $fasta_file.out
done