No, your e-mail account has not reached a maximum size. The sender of this email is a fraudster who wants to steal the access data to your email account. His server is located in the USA.
The perpetrators are acting under the domain reg3.xyz, which has been hosted via the ISP namecheap.com. It should not take long until this ISP blocks the server, with the expected consequence that the perpetrators will switch to another service.