buscar la mail.activity que se envía al usuario que va a aprobar

# Get current user 
user_id = context.getUser()

# Get the user's mail
user_mail = user_id.getProperty('email')

# Get all mail.activity that are asigned to the current user
mail_activity_list = self.env['mail.activity'].search([('user_id', '=', user_id.id)])

# Iterate over mail.activity list and return the one that contains the current user's mail
for mail_activity in mail_activity_list:
    if ('<div>' + user_mail + '</div>') in mail_activity.note:
        return mail_activity