If you find yourself in the situation that you are in Germany using Germany Telekom and their bundled Internet security router. This router does not allow you to send out e-mails, here an easy way to solve the problem
Login on http://speedport.ip in your Web browser (or directly the IP address something like 192.168.2.1). If you or the person responsible for the router did not change the password, it is in the line below speedport.ip. Then you have to go to Internet -> E-mail abuse detection and disable use e-mail abuse detection OR you can add mail.psmail.net to the whitelisted servers on your router.
Content provided courtesy ofย ย http://k7r.eu/telekom-router-blocks-mail-servers/