code: func (perm *SESPermission) NewMessageBodyStorageReference(prexistingBucketName string) (*MessageBodyStorage, error) {
  	store := &MessageBodyStorage{}
  	store.bucketNameExpr = gocf.String(prexistingBucketName)
  	return store, nil
  }
docs: // NewMessageBodyStorageReference uses a pre-existing S3 bucket for MessageBody storage.
  // Sparta assumes that prexistingBucketName exists and will add an S3::BucketPolicy
  // to enable SES PutObject access.