@pepe84 @TheOtterslider I'm using 1and1 on one of my subsidiary sites as well and had issues ages ago. I did eventually change the settings to those below and found that they finally worked:
SMTP host: smtp.1and1.com
SMTP username: email@domainname.com
SMTP port: 25
Secure connection: no
Not as ideal from a security perspective, but at least they did go through.