22-year-old Eastwood was shown a straight red by referee Paul Melin after he pushed Terriers defender Andrew Holdsworth in the chest.
Our sister site, The Little Gazette,commented on his actions with: "He has no-one to blame but himself."
Eastwood was handed an automatic three-match ban, but this was delayed due to the Shrimpers' appeal and did not include Tuesday night's loss to Southampton in the Carling Cup.
But the appeal has backfired on the Roots Hall club, as the Football Association have upheld the ban - and extended it to include four games.
So as well as missing Friday's game at Glanford Park, Eastwood is also ruled out of their League games against Colchester, Oldham and Swindon.