How to categorize unlabelled promotional email data
So the question asks what model can you use to put texts into topic categories in a unsupervised way.
The main model that we use for this sort of task is Latent
Dirichelt Allocation (LDA) (https://programmerbackpack.com/latent-dirichlet-allocation-for-topic-modelling-explained-algorithm-and-python-scikit-learn-implementation/)
Also, there is another method you could try, which is to convert texts into document embedding using a Doc2Vec (https://medium.com/wisio/a-gentle-introduction-to-doc2vec-db3e8c0cce5e) model, which will convert the text into an n dimensional vector. From these document embedding you could use any form of clustering (KNN or Agglomerative Clustering) to cluster the texts into topics.