Their latest exchange relates to a Cattrall family tragedy.
Her brother had gone missing earlier this month and was later found dead on his rural property in Alberta, Canada, according to local officials.
Soon after his death was announced, Cattrall took to Twitter to thank her followers and her former castmates for their support.
"I would like to thank my fans, friends, and my #SexandtheCity colleagues for the outpouring of support for myself and family over the past 72 hours," Cattrall tweeted.
Later, the actress posted an image on Instagram reading, "I don't need your love or support at this tragic time @sarahjessicaparker."
"My Mom asked me today 'When will that @sarahjessicaparker, that hypocrite, leave you alone?,'" Cattrall wrote in the caption of the photo. "Your continuous reaching out is a painful reminder of how cruel you really were then and now."
"Let me make this VERY clear. (If I haven't already) You are not my family. You are not my friend," she added. "So I'm writing to tell you one last time to stop exploiting our tragedy in order to restore your 'nice girl' persona."
Cattrall also shared a link to an October 2017 New York Post story titled "Inside the mean-girls culture that destroyed 'Sex and the City'."
Here's the sad history of their estrangement:
Parker long denied that there was an issue
There has been chatter for years that the two women did not get along while working together, but Parker said that was not the case.
"It used to really confound me and really upset me because we were part of a family of 'Sopranos' and nobody ever questioned the relationships of the men on that show," Parker told Howard Stern in 2016. "No one ever said to them 'Did you hang out this weekend with each other?" or 'Did you give each other Christmas presents?'"
Parker said the speculation was often based on rumors of misbehavior on set.
"I take very seriously my reputation," she said. "I work really hard and I treat people well...I have a work ethic that's very meaningful to me, and it's based on the affection I feel for the people I get to work with."
In September 2017, Parker confirmed that "SATC 3" would not be happening.
"We had this beautiful, funny, heartbreaking, joyful, very relatable script and story," she said. "It's not just disappointing that we don't get to tell the story and have that experience, but more so for that audience that has been so vocal in wanting another movie."
Cattrall was not feeling the love
The following month during an interview with Piers Morgan, Cattrall said she didn't appreciate being held responsible for holding up a third "SATC" film.
The actress said she made the decision in 2016 that she did not want to be involved in any more sequels.
It had nothing to do with demands for money or more scenes, she said.
"This is about a clear decision, an empowered decision in my life, to end one chapter and start another," she said.
At 61, Cattrall said, she's 10 years older than Parker and fellow cast members Kristin Davis and Cynthia Nixon and feels simply done with the franchise.
Cattrall also said she's not been in contact with the women.
"We've never been friends," she said. "We've been colleagues and in some ways that's a very healthy place to be because then you have a clear line between your professional life and relationship and your personal."
Parker was hurt
Parker recently told friend Andy Cohen on his Bravo talk show that she was "heartbroken" over Cattrall's comments.
"I found it very upsetting cause that's not the way I recall our experience," Parker said.
CNN has reached out to reps for both actresses for additional comment.