smtp session via telnet with bad HELO

$ telnet relay.plus.net 25
Trying 212.159.8.107...
Connected to relay.plus.net.
Escape character is '^]'.
220 avasout06 smtp relay.plus.net
EHLO mymac.mydomain\.co\.uk
501 EHLO requires valid address
RSET
250 OK
HELO mymac.mydomain\.co\.uk
501 HELO requires valid address