mailcap on Windows WSL

Good morning,

I need to use mutt within the WSL of MS Windows. To display HTML
mails via mailcap, I created a small script which reads from STDIN,
writes a temporary file and opens it with the Edge browser:

# ~/.mutt/mailcap
text/html; ~/.mutt/htmlviewer html

# ~/.mutt/htmlviewer
with open('/var/tmp/htmlfile', 'w') as tmp_file:
	for line in sys.stdin:
		tmp_file.write(line)

This works for some messages, but for others, a UnicodeEncodeError is
returned:

'utf-8' can't encode character '...' in position ...: surrogates not
allowed

Since all of the messages affected were encoded in iso-8859-1, I tried
this (temporarily, with the intention of reading %{charset} from mutt
into the script later):

with open('/var/tmp/htmlfile', 'w', encoding='iso-8859-1') as tmp_file:
	...

but this only changed the error message to:

'latin-1' can't encode character '...' in position ...: ordinal not in
range(256)

How can I reliably write the input provided by mutt to a temporary file?

- Jan

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