Complex sentence: Because UUNET started with a loan from Usenix and controlled the e-mail addresses for moderated Usenet groups, it was hard to block Usenet from and/or e-mail traffic to it.
Split into simpler sentences: Because UUNET started with a loan from Usenix and controlled the e-mail addresses for moderated Usenet groups. As such, it was hard to block Usenet from and/or e-mail traffic to it.