Most JonDonym Mixes block sending E-Mails over E-Mail programs. This is mainly for protection against spam, but also because E-Mail programs might leak information about you and your hardware. However, JonDonym services with SOCKS support allow your program to receive E-Mails:

• Install and run Thunderbird and the profile switcher extension, or run Thunderbird portable.
• Create a new Thunderbird profile, named "anonymous". If you already have a Thunderbird profile, you may do this by using the profile switcher extension, or by starting a second installation of Thunderbird portable.
• Set ALL Thunderbird proxies to host=127.0.0.1, port=4001 (Tools->Options->Advanced->Network->Connection button)
• Switch network.proxy.socks_remote_dns to true in Thunderbird settings (Tools -> Options -> Advanced -> General -> Config Editor button)
• Create a pseudonymous E-Mail account with POP support. Choose an E-Mail adresses of the form anonymous1234abcd@xx.yy, that is "anonymous" + numbers + letters. If all JonDo users create addresses of this form, they are much less distinguishable.
• Now enter the POP information from your E-Mail account in Thunderbird. Try to receive E-Mails, and watch whether JonDo really transfers data. If it does not, use this account for testing only, and create a new one! Otherwise the E-Mail provider has your IP address!