\usemodule[letter]

\startletter
   [subject={How to change the position of the subject line},
    opening={Hi Parchd,}]

The elements of the letter environment can be changed with the 
\tex{setupletterelements} commands,
the default order of them is

\startitemize[packed]
\item title,
\item subject,
\item opening,
\item content,
\item closing and
\item appendices
\stopitemize

To put the subject after the opening you have to modify this order with 
the following setup:

\starttyping
\setupletterelements
   [section]
   [title,
    opening,
    subject,
    content,
    closing,
    appendices]
\stoptyping

\stopletter

Wolfgang

> Parchd <mailto:parchd@archlinux.info>
> 1. September 2017 um 13:04
> British letters typically have the subject below the opening.
>
> A stackexchange user asked many moons ago how to accomplish this in
> ConTeXt, and received a rather hackish response
> (https://tex.stackexchange.com/questions/22438/how-to-place-the-subject-line-under-the-greeting-line-in-t-letter-module-in-cont).
>
> ConTeXt and the letter module have changed a lot since then, if my
> experience is correct. Is there a better solution than given there?
>
> Best,
>
> Parchd.
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