Mail (POP3/IMAP) using STARTTLS

[Felix Natter]

hello,
I am using STARTTLS to connect to my institution's smtp-server:

(setq smtpmail-starttls-credentials
      '(("smtp.inf.fh-bonn-rhein-sieg.de" 587 "" "")))

(setq mail-sources
      '((imap :server "imap.inf.fh-brs.de"
              :stream ssl
              :user "fnatte2s"
              :password "XXX")))

(but I'd be happy with POP3 as well)

However, I don't have a certificate, I'd like to authenticate via
username/password. Unfortunately, smtpmail.el says:

smtpmail-starttls-credentials is a variable defined in `smtpmail.el'.
Documentation:
Specify STARTTLS keys and certificates for servers.
This is a list of four-element list with `servername' (a string),
`port' (an integer), `key' (a filename) and `certificate' (a filename).

How can I do this?

thanks,         

-- 
Felix Natter