How would you classify an email signature using NLP?

This is a challenge I have been working on for a few days now.

I have 150gb of mail that I will try to work with from an NLP perspective.

I wish to do some different classification with the emails.

But the first fun thing I ran into was how I need to classify the signature in an email.

I ended up manually picking around 500 email signatures and trained a model for recognition. My model performs horrible.

How would you do that ?