added SPFToolbox

README.md

@@ -507,6 +507,7 @@ _Recipe management_
 See https://github.com/n1trux/awesome-sysadmin#dns
 
   * [nsupdate.info](https://www.nsupdate.info/) - nsupdate.info is a dynamic DNS service. ([Demo](https://www.nsupdate.info/account/register/), [Source Code](https://github.com/nsupdate-info/nsupdate.info)) `BSD` `Python`
+  * [SPF Toolbox](http://spftoolbox.charlesabarnes.com) - selfhosted free replacement for Mxtoolbox ([Demo](http://spftoolbox.charlesabarnes.com), [Source Code](https://github.com/bulbajackel/SPFtoolbox)) `MIT` `PHP`
 
 ## Document Archiving