Thanks everyone for the responses. It seems that forcing clients to use a particular ticket system is not a good idea. I have now created a free account at Hub

Thanks everyone for the responses. It seems that forcing clients to use a particular ticket system is not a good idea. I have now created a free account at Hubspot. Hubspot keeps track of all e-mails and calls I make to people and I can automatically add notes and tasks to each form of communication.