rejected EHLO from localhost [127.0.0.1]: syntactically invalid argument(s): (no argument given)
After changing my hostname from abcd to abcd.myexample.com, I started to get entries like above when sending mail right there in the server, no such error if the mail is sent via smtp relay even the client machine is ssh tunneled into the server and using localhost as smtp name.
This should work: helo_allow_chars = .
but I used a simpler appraoch, changed the host name to myexample.com
Note: resetting machine will cause the hostname to go back to the old one, one way is: vi /etc/hostname