Amazon S3 bucket names are UNIQUE accross all AWS Accounts. For example, suppose your first account username is acc1@gmail.com and second is acc2@gmail.com.

#s3cmd –configure : Configure for acc1 aws account

and create similar bucket (not same bucket name) in the acc2 account and set those bucket permissions to (Gurantee=)Everyone – (Tick)Upload/Delete.

Then you can use s3cmd (using the credentials of the acc1) to do something like:

s3cmd cp s3://acc1_bucket/folder/ s3://acc2_bucket/folder -r

All transfer will be done on Amazon’s side.