Companies provide points of contact for these types of legal process to be served on them - it is akin to the registered agent process. Govt agencies do not have the authority to dictate how a company accepts this legal process, only that they comply with the legal order itself. As a result, govt agencies follow the methods of contact that a company provides, whether its a fax number, email address, mailing address, etc.

Agencies are willing to follow the process that a company lays out because it makes engaging with that company easier. It is not in an agency's interest to make the process difficult (i.e. demanding to use fax machines when a company already has a [email protected] email set up).