FIRM, POSITIVE, PROFESSIONAL & FOCUSED ON FACTS
You shipped parts to your customer.
Your customer sends you an email which is copied to "the world" condemning your parts and chastising your company.
Don't become angry. Don't speculate about what is going on. Don't make any assumptions. Don't conjure up conspiracy theories. Don't rush to fix something when you don't even know what, if anything is broken!
This is not personal; it's business. Focus on establishing the facts.
1. Did you ship the parts called out on the purchase order; part number and revision level? Did you complete the inspection plan called out by the control plan? Is everything documented properly? If the answer is yes to all of these questions then you need to dig deeper.
2. Talk to your customer. What exactly is the reason for the complaint? Are we talking about a dimension or feature that is not on the drawing? Has the customer changed something? For example is this part going into a different application? What needs to be done so that the customer will be satisfied with your parts?
3. Once you have established the facts, communicate them to your customer contacts without any editorial comment. Keep the emotion out of written correspondence. Clearly identify all options as well as any cost and timing impacts. Make your recommendation.
Stay firm, positive, professional and focused on facts. Very often you will find that you didn't do anything wrong at all. This gives you an opportunity once again to proactively help your customer. That is a good thing!
