the variable "MyHostname" points to localhost by default and I don't know what it must be. Currently the SMTP server replies: '554 <127.0.0.1>: Helo command rejected: You are not me'.

The SMTP server needs you (the client) to identify yourself. That's done by telling your domain name. PoCoClSMTP is dumb enough not to know how to do that so it let's you do that :)

That means you need to provide it with your domain name (using MyHostname).

Of course, if you are not able to determine your domain name, or the domain name doesn't mean nothing, you can provide your IP address to the SMTP server in the form: [XXX.XXX.XXX.XXX] provided via MyHostname