The player was fined for failing to disclose his wife was driving his car when it was caught speeding on the A66 at Appleby.
He claimed he missed notices of prosecution because he was away from his Billingham home for three months.
Carlisle magistrates told the 29-year-old, who is on loan at Marseille, he needed to organise his post better.
The footballer was fined £1,000 and given six penalty points. He was also ordered to pay £620 costs and a £100 surcharge.
The court heard he was sent several letters requesting information on who was driving the car and given notice of an intended prosecution.
He had denied failing to disclose the information but magistrates found him guilty after a two-hour trial concluded he should have had a more effective system for dealing with post in his absence.
Fletcher signed for Sunderland from Wolverhampton Wanderers for £12m in 2012 and went on to score 23 goals in 94 games for the Black Cats.
He joined Marseille on loan in January and has scored two goals in 12 games.
Sunderland striker Steven Fletcher has been told off by the courts for not managing his mail properly.