Yes it is extremely important to know how to manage disputes and conflict. But, I have mentionned it before in my post, it is very very important that you keep a level head.
Don't imitate the language or abusive tone the user is giving you. Stay professional. Stay detached. Refer to your terms and conditions and any previous communications about the topic. Make clear that you are keeping a record ( you can create a folder in your outlook for that topic and print it for your records). Try to get to the underlying problem.
They might be pissed off about their e-mail servers not working. Even if you copy paste the configuration e-mail to them twelve times, it might just be a comprehension problem. Sometimes re-wording the information or offering to send it in another language (if possible, if you know people that speak other language and owes you a favor :-)).
Not everyone is well versed into this hosting business. You cannot assume that all your clients are at the same level. As long as you offer to help, stay respectful and use a professional tone, you are doing a good job. You can prove to other parties that you have followed strict guidelines established by your company and that you have offered several options.
Hope this adds insight.