advertise who we are in the SMTP 220 banner

scripts/mail.sh

@@ -63,10 +63,11 @@ tools/editconf.py /etc/postfix/main.cf \
 
 # Have postfix listen on all network interfaces, set our name (the Debian default seems to be localhost),
 # and set the name of the local machine to localhost for xxx@localhost mail (but I don't think this will have any effect because
-# there is no true local mail delivery).
+# there is no true local mail delivery). Also set the banner (must have the hostname first, then anything).
 tools/editconf.py /etc/postfix/main.cf \
 	inet_interfaces=all \
 	myhostname=$PUBLIC_HOSTNAME\
+	smtpd_banner="\$myhostname ESMTP Hi, I'm a Mail-in-a-Box (Ubuntu/Postfix; see https://github.com/joshdata/mailinabox)" \
 	mydestination=localhost
 
 # Handle all local mail delivery by passing it directly to dovecot over LMTP.