  This paper presents a \emph{non-instant field model} for electrodynamics that
permits a causal explanation of the \emph{Aharonov-Bohm effect} and a
\emph{covariant quantization} of the respective Maxwell equations via the
\emph{Gupta-Bleuler method}. Our model satisfies the following
\emph{correspondence principle}: if $A^\mu$, $\vE$, $\vB$ denote the four
potential, the electric field and the magnetic field of the non-instant field
model, then the respective classical quantities are $\A[A^\mu]$, $\A[\vE]$,
$\A[\vB]$, where $\A$ is a covariant time averaging operator. Here $\A[A^\mu]$
is interpreted as the best possible measurement of the four potential $A^\mu$.
Although the Lorentz condition is not satisfied for $A^\mu$, it is satisfied
for $\A[A^\mu]$. The latter fact means that the Lorentz condition does not hold
for the quantized field but for its expectation value (cf. \emph{Gupta-Bleuler
method} of quantization). Finally, we derive the energy conservation law of our
field model and show that the field energy is quantized.
