Helo with localhost

[phocean]

It opens SMTP connections with the hardcoded "localhost" string.

helo localhost

Then, it shows in message sources:

Received: from localhost (xxx])
    by xxx
    for xxx

Which gets flagged by many anti-spam:

X-Spam-Status: No, score=4.53 ....
    ...
    HELO_LOCALHOST=3.828, ...

My hostname is configured properly on my machine. I also checked with this simple script:

package main

import (
        "fmt"
        "os"
)

func main() {
        fmt.Println(os.Hostname())
}