I've built and worked on this exact problem before at bigtech, startup and personal projects. Regex works well if you have a very limited set of sender and rec

I've built and worked on this exact problem before at bigtech, startup and personal projects. Regex works well if you have a very limited set of sender and recipient accounts that don't change often Bayesian or DNN classifiers work well when you have labeled data. LLMs work well when you have a lot of data from lots of accounts. You can even combine these approaches for higher accuracy