A look at the new sides the O's will be coming up against next seasonOrient will face new opponents in the shape of Blackpool, Crewe Alexandra, Colchester United and Doncaster Rovers who were all relegated from League One, while the Mariners are joined back in the Football League by Cheltenham Town.
Here we give a rundown on when we will face those sides:
BLACKPOOL (Home - November 19, Away - May 6, 2017)
Manager: Gary Bowyer
League Position: 22nd, League One
O’s League Record: Won 21 Drawn 17 Lost 31
Last Time We Met: 20/1/2007 L 1-0 The O’s lost out 1-0 after Keith Southern’s strike five minutes from time at the Matchroom Stadium
Blackpool have suffered a second successive relegation after finishing their first season back in League One in 23rd position under Neil MacDonald, who was sacked last week as a result.
The Tangerines amassed only 46 points throughout the 2015-16 campaign, and will be hoping to bounce back at the first opportunity having been in the Premier League only five years ago.
CHELTENHAM TOWN (Away - August 6, Home - February 25)
Manager: Gary Johnson
League Position, 1st, National League
O’s League Record: Won 6, Drawn 4, Lost 8.
Last Time We Met: W1-0, 4/04/09. Dean Morgan’s 25th minute strike at Whaddon Road was enough to secure the O’s all three points.
The Robins bounced back from relegation at the end of 2014-15 season in fine style by securing promotion back to the Football League at the very first attempt under boss Gary Johnson.
They picked up 101 points in the promotion-winning season and striker Dan Holman finished joint top goalscorer with 30 on their way to the title.
COLCHESTER UNITED (Away - November 12, Home - April 29)
Manager: John McGreal
League Position: 23rd, League One.
O’s League Record: Won 12, Drawn 13, Lost 19.
Last time out: L 2-0, 24/01/15. Goals from Gavin Massey and Kaspars Gorkss saw the O’s on the wrong end of a 2-0 scoreline at the Weston Homes Community Stadium, despite the hosts being reduced to 10 men seven minutes from time when Elliot Hewitt was dismissed.
The U’s eight-year stay in League One came to an end as they finished bottom of the division.
The Essex side started the campaign with Tony Humes in charge, but he was replaced by Kevin Keen, and despite a run of four wins in eight games in March and early April, it was not enough to secure their survival.
Keen left his position following relegation and has been replaced by former Ipswich Town defender John McGreal.
CREWE ALEXANDRA (Home - October 29, Away - April 22)
Manager: Steve Davis.
League Position: 24th, League One.
O’s League Record: Won 12, Drawn 9, Lost 7.
Last time out: D 1-1, 11/04/15. The O’s picked up a point from their visit to Gresty Road. The Railwaymen took a 10th minute lead through Lauri Dalla Valle, before Darius Henderson levelled matters on the half hour mark.
Crewe Alexandra finished bottom of League One last term, bringing to an end a four-year stay in the division.
Under Steve Davis, who took over from Dario Gradi MBE in 2011, the Railwaymen picked up just seven wins and accrued 34 points in total.
DONCASTER ROVERS (Away - November 26, Home - March 18)
Manager: Darren Ferguson
League Position 21st League One
O’s League Record: Won 13, Drawn 6, Lost 11
Last Time Out: L 1-0. 14/04/15. Rob Jones’ second half header saw the visitors come away with victory.
Darren Ferguson’s side were unable to avoid the drop back into League Two for the first time since winning the then Third Division in 2004.
Ferguson moved to the Keepmoat Stadium in September, signing an x-year deal after Rob Jones had a short spell as caretaker following the dismissal of Paul Dickov.
Rovers have wasted little time in strengthening their squad this summer with the signing of former Peterborough United midfielder Tommy Rowe on a three-year deal.
GRIMSBY TOWN (Away - August 20, Home - March 11)
Manager: Paul Hurst
League Position: 4th, National League.
O’s League Record: Won 16, Drawn 14, Lost 20
Last Time Out: D 0-0. 17/04/06. In the O’s 2005-06 promotion-winning season, Martin Ling’s side picked up a goalless draw.
Grimsby ended their six-year Football League absence with a 3-1 Play-Off Final win over Forest Green Rovers.
Two goals from Omar Bogle put them in the box seat, before Keanu Marsh-Brown pulled one back for Rovers. However, the Mariners sealed the victory when Nathan Arnold netted a late third.
Grimsby had finished the regular campaign in fourth spot, and beat Braintree Town 2-1 on aggregate to seal their second successive Play-Off final appearance, after losing out on penalties in 2014-15 to Bristol Rovers.