Any "rough ideas" anyone could have will be proven wrong sooner or later anyway, so the answer is: No. There hasn't a been a single beta version after the current public release. Mercury v5 will be the first one to come within the next months, but don't hold your breath.
[quote user="lhhesscpa"]When I receive an especially important email, one that requires priority attention, I manually apply the Urgent tag so that it is placed at the top of the list of in the inbox. So an automatic rule is not a solution for my needs.[/quote]
I don't know of a way to change the urgent color. You might be able to accomplish what you need by marking as unread and and then setting a color. This won't keep the message at the very top of the list but it may keep it high enough.
AFAIK, the font button on the new message toolbar is specific to that message. The one in the main window toolbar sets the default for the active window. Also, default fonts are identity specific.
Keep in mind that the recipients font settings will dictate how it's displayed on their end unless you are sending formatted html. That's a frustration for me. My emails routinely contain lines with numbers so I send in a mono-spaced font. Number alignment looks good when I hit send but it's usually a mess when quoted in a reply. The use of a table helps but requires too much effort just to send a few short lines containing text and numbers.
If they're in the new mail folder you would use a new mail filtering rule > rules applied when folder is opened. All unread messages will be run through the filter each time the new mail folder is opened. Note that only unread message are filtered so you may have to mark them as unread. You can mark all as unread using Ctrl + A followed by Ctrl + U.
If they are in a folder you would use a general rule set and attach it to the folder as a folder-open or folder-close filter set. The attach option is in the context menu when your right-click on a folder name. The read/unread status is irrelevant in this scenario.
If you haven't worked with filters before consider testing the filter using a "Set message colour" action. This provide visual verification of the messages detected by the filter. If all is well you can then change the action to Move or Delete.
RESOLVED: My website host's ISP mailserver suddenly started rejecting my emails--even with SSL certs in place. Host added SPF authentication for my domains, problem went away.
It still begs the question why they would refuse a message with ASCII content. I would be very interested to understand why they block this. The pessimist in me suspects it is a knee-jerk reaction.