Updated labels in config page

setup/templates/steps/config.html

@@ -7,20 +7,27 @@
   <input class="form-control" type="text" name="root" value="/mailu" required pattern="^/[-_A-Za-z0-9]+(/[-_A-Za-z0-9]*)*">
 </div>
 
+<p>In the next sections we need to set the postmaster address. This is a combination from the <i>postmaster</i> local part and the <i>main mail domain</i>.
+The <i>main mail domain</i> is also used as </i>"server display name"</i>. This is the way the SMTP server identifies himself when connecting to others.
+The Postmaster will get an e-mail address &lt;postmaster&gt;@&lt;main_domain&gt;. This address will receive the DMARC "rua" and "ruf" reports.
+Or in plain english: if receivers start to classify your mail as spam, this postmaster will be informed.</p>
+
 <div class="form-group">
-  <label>Main mail domain</label>
+  <label>
+    Main mail domain and server display name.
+  </label>
 <!--   Validates domain name -->
   <input class="form-control" type="text" name="domain" placeholder="e.g. mailu.io" 
   		required pattern="^([a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,}$">
 </div>
 
 <div class="form-group">
-  <label>Postmaster local part (will append the main mail domain)</label>
+  <label>Postmaster local part</label>
   <input class="form-control" type="text" name="postmaster" value="admin" required>
 </div>
 
 <div class="form-group">
-  <label>Choose how secure connections will behave </label>
+  <label>Choose how you wish to handle security (TLS) certificates</label>
   <br/>
   <select class="btn btn-primary dropdown-toggle" name="tls_flavor">
   	{% for tlsflavor in ["letsencrypt", "cert", "notls", "mail", "mail-letsencrypt"] %}