On January 11, Sister Mary Mark of St. Paul, Minnesota, celebrated her 105th birthday. But her longevity isn’t just the most surprising thing about her.

She has spent over 20 years of her life sending letters of encouragement to inmates in correctional facilities.

Sister Mary Mark, who has been a nun for more than 80 years, started the project after she responded to a notice in a newspaper calling on pen pals for prison inmates.

“She says she just offers [the inmates] love and encouragement and lets them know they are not alone,” Kathleen Conrad, pastoral care coordinator of Carondelet Vilage in St. Paul where Sister Mary Mark lives, told Good Morning America in an interview.

“When she was 89 years old she was called down to Oklahoma to testify on behalf of a prisoner on death row because she had been writing to him for such a long time,” Conrad shared.

Sister Mary Mark currently corresponds with three prisoners. Their photos hang on her bulletin board.

“I surely do [enjoy] writing the letters and I’ve been doing it for many years,” Sister Mary Mark said. “They’re in prison, but they’re working. They hope to make it. Other people have asked me for names, so that they could write to them [the inmates] too.”

“She’s very concerned as to what will happen when she’s not writing to them anymore,” Conrad said.

Should the day come when Sister Mary Mark becomes unable to write those letters, Conrad said Mary Lou Carney, a volunteer at Carondelet Village, will take over writing the letters.

But there seems to be no signs of slowing down for the centenarian, who says, “”as long as I can write, I’ll do it.”

There are websites that offer similar correspondence, such as Meet-An-Inmate.com which “has been helping male and female inmates connect with the outside world since 1998 and is ranked #1 among prison pen pal websites.” There are also WriteAPrisoner.com, FriendsBeyondTheWall.com, and LostVault.Com.

Aside from easing loneliness for those who are behind bars, pen pal services for inmates exist because they help inmates keep a positive attitude, focus on the future, find jobs and housing upon release, improve their education, and become contributing members of society.

According to WriteAPrisoner.com, “people from all walks of life choose to correspond with prison pen-pals.” Among those who have chosen to be pen-pals for inmates are “U.S. military personnel stationed overseas, attorneys, pen-pals of every religious affiliation, estranged family members, and world citizens.”

Here is Sister Mary Mark celebrating her 105th birthday!

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[Image from CSJ St. Paul/YouTube]