Logjam is a bug that existed since the 1990s. It would allow an attacker sitting between a user and a vulnerable server to lower the TLS encryption so that it can be cracked. The bug affects all servers that support DHE_EXPORT ciphers for encrypting their traffic. The Tutanota servers never supported DHE_EXPORT and, thus, were never affected by Logjam.
As a precaution we have configured the Tutanota servers so that they do not support any DHE cipher suites at all. Thus, we even protect your unencrypted emails with secure transport encryption.