Hi,
Caused by: javax.mail.MessagingException: Could not connect to SMTP host: smtp.web.de, port: 465;
First of all you have to be sure this machine could access the mail server on the port 465
please check if the mail server could be accessed from the machine where you have installed Activiti.
(you could use telnet.. or whatever you prefer)
If you are able to access it from this machine and send a new email message from telnet, then the problem moves to configurations.