importer/archiver does not unwrap header lines before storing in mbox

When emails are parsed, line-wraps and ignorable white-space should be removed before storage in mbox fields.

It looks like this is not happening.

Start by locating the importer/archiver code that parses email headers and stores fields in mbox. Reproduce an email with wrapped header lines and ignorable whitespace, then verify that stored mbox fields contain unwrapped, trimmed values; the issue names no specific file or test.

Written by the indexing model from the issue text.