This feels like a diagnosis without evidence. Why do you believe the hex noise in the reply-to email is the reason that Outlook.com is marking these messages as SPAM? There are many other possible reasons. I suggest that you investigate the situation with Outlook.com tech support before proposing solutions. The proper solution may be something else entirely. Emails from SQLite.org don't appear to be using DKIM, for example, and Outlook.com may be downgrading all email that lack DKIM signatures. (...Which is one of many reasons why "just make Fossil forums support inbound email" is a trivial response to a non-trivial problem.)