"Created by" field of CiviMail pulls the name of the latest subscriber
CiviCRM 4.6 has not been supported for some time. It has known security issues and PHP compatibility issues.
There may still be people in the community with CiviCRM 4.6 sites who can assist in troubleshooting but you should absolutely raise within your organisation that they should be upgrading CiviCRM to a supported version.
The end of life for CiviCRM 4.6 and 4.7 was announced on 2018-12-02 here: https://civicrm.org/blog/josh/extended-security-release-update