What is found in Mr.____’s trunk? What is symbolized by the trunk and the objects found inside?

For most of The Color Purple, the narrator, Celie, lives under the thumb of her abusive husband, Mr.——. She and her younger sister, Nettie, the person she cares about most in the world, are also separated for many years.
Celie is afraid that Nettie is dead, because she is sure that if Nettie were alive she would try to reach out to Celie. With the help of Shug Avery, Celie discovers that Mr.—— has been hiding letters from Nettie to Celie in his trunk. Reading the letters, Celie finds out that this is because, years ago, Mr.—— tried to rape Nettie. Because Nettie fought him off, he told her that she would never see Celie again.
There are probably multiple reasonable interpretations as to what the trunk and the hidden letters symbolize. I see it as being symbolic of women being silenced by men, which happens quite a lot in this book. After she is able to open up to Shug about her life, Celie starts to communicate more and becomes a stronger person. But before that, Celie is a very quiet person, abused and silenced by her stepfather and then Mr.——. By hiding the letters, Mr.—— not only keeps Nettie's voice silent, but also worsens his silencing of Celie, because she had believed she had no one in life who cared for her. The opening of the trunk and discovery of the letters push Celie to end her silence.