Mail-in vote clearly has a hard swing Dem, like other states with small % of mail-in vote relative to total vote.
Harrison County mail looks like Biden+28 (Biden 8939 Trump 5111) even though it was Trump+37 end of election night result. Some counties have absolutely no mail-in vote reported, while others have partial or near complete counts.
On average it looks like Trump's margin is 2% worse in counties that are currently greater than their 2016 vote totals, so I think it's reasonable to think MS ends up swinging in the end, with a chance of trending D as well.