James Thomas wrote:

> +	(if (not nnmail-use-long-file-names)
> +            (nnheader-replace-chars-in-string group ?. ?/)
> +	  group))

Since directory names cannot have '/' they used to be replaced by '_' in
group names before conversion. But this makes it impossible, when
generating (non-existent) active files to know whether a '_' in the
directory name was _ or / originally.

The above patch tries a possible solution inspired from [1] but would
break existing users of the cache or agent (xref-find-references
"nnmail-group-pathname") who have groups with % or / in their names.

Seems to work in my limited testing. WDYT?

Regards,
James

1:
https://stackoverflow.com/questions/9847288/is-it-possible-to-use-in-a-filename#answer-9847319