[MlMt] MailMate width

[John Cooper]

Roger Sheen wrote (at 8:47 AM on Sunday, Dec12, 2021):

> Instead of splitting the current window width in two as expected, the Preview pane increases the window size, pushing the right side beyond the display boundaries.

I can confirm this, but not this:

> When you edit to remove the Markdown syntax, the Preview disappears again, but instead of restoring the original window size, it reverts to half of that.

I'm using build 5852 on Mac OS Monterey 12.0.1.