add a note on the aliases page that aliases should not be used to forward to outside domains

fixes #1198

CHANGELOG.md

@@ -13,6 +13,7 @@ Control Panel:
 * The users page now documents that passwords should only have ASCII characters to prevent character encoding mismaches between clients and the server.
 * The users page no longer shows user mailbox sizes because this was extremely slow for very large mailboxes.
 * The Mail-in-a-Box version is now shown in the system status checks even when the new-version check is disabled.
+* The alises page now warns that alises should not be used to forward mail off of the box. Mail filters within Roundcube are better for that.
 
 v0.29 (October 25, 2018)
 ------------------------

management/templates/aliases.html

@@ -39,8 +39,9 @@
     <label for="addaliasForwardsTo" class="col-sm-1 control-label">Forwards To</label>
     <div class="col-sm-10">
       <textarea class="form-control" rows="3" id="addaliasForwardsTo"></textarea>
-      <div style="margin-top: 3px; padding-left: 3px; font-size: 90%" class="text-muted">
-        <span class="domainalias">Enter just the part of an email address starting with the @-sign.</span>
+      <div style="margin-top: 3px; padding-left: 3px; font-size: 90%">
+        <span class="domainalias text-muted">Enter just the part of an email address starting with the @-sign.</span>
+        <span class="text-danger">Only forward mail to addresses handled by this Mail-in-a-Box, since mail forwarded by aliases to other domains may be rejected or filtered by the receiver. To forward mail to other domains, create a mail user and then log into webmail for the user and create a filter rule to forward mail.</span>
       </div>
     </div>
   </div>