The header information generated by Mail step does not comply the RFC2822 (https://www.ietf.org/rfc/rfc2822.txt). The header information of email should comply RFC2822, which specifies the internet mail format including header information. However, the header information generated by Mail step does not comply the RFC. As this is not RFC incompliant, the sender-name is garbled.
According to the RFC2822, the Internet mail messages including header information should be made up of US-ASCII characters. (See 2.1. General Description in the RFC) And also, in order to use non-ASCII characters in header information, the text should be encoded according to RFC2047. So with strict mail servers, we can notice that Sender Name contains garbled characters.