  In this work quantum electrodynamics at T > 0 is considered. For this purpose
we use thermo field dynamics and the causal approach to quantum field theory
according to Epstein and Glaser, the latter being a rigorous method to avoid
the well-known ultraviolet divergencies of quantum field theory. It will be
shown that the theory is infrared divergent if the usual scattering states are
used. The same is true if we use more general mixed states. This is in
contradiction to the results established in the literature, and we will point
out why these earlier approaches fail to describe the infrared behaviour
correctly. We also calculate the thermal corrections to the electron magnetic
moment in the low temperature approximation k_B T << m_e. This is done by
investigating the scattering of an electron on a C-number potential in third
order in the limit of small momentum transfer p -> q. We reproduce one of the
different results reported up to now in literature. In the low temperature
approximation infrared finiteness is recovered in a very straightforward way:
In contrast to the literature we do not have to introduce a thermal Dirac
equation or thermal spinors.
