The worst thing about a rude message is the author presuming you'll respond to a complaint or request when his communication lacks any hint of civility.
When confronted with an obvious violation of good manners, you can easily delete the email without upsetting anyone who is aware of politeness standards. You can also punt the request to a co-worker, but that would make you the bad guy. It's best to respond but take certain steps to ensure your response is a solicitous one, and then move on to other, more pleasant tasks.
Delay Your Response to the Email
To ensure you don't send a scathing reply in response to the offensive email, close the message after you read it, flag it for follow-up and move on to another task. This will help you focus on something else, rather than sit and simmer about the rude email. When you deal with the message later, after you've had a chance to separate the subject of the message from its tone, you'll be better prepared to create a congenial and rational response, rather than an emotional one.
Use the Text Expansion Utility
If you can't just delete the rude email, but rather must issue a response, don't over-invest in the process. The text expansion utility can help you in this regard. The utility will automatically enter long blocks of text that you create in advance based on a few keystrokes that you type. By limiting the time you commit to your response, your emotional investment will be less as well.
Create a Neutral Response
It might be tempting to send a rude email in return, but remember the goal of the sender may have been to get your attention and perhaps make you angry – so it's best to ignore the person and handle the issue. If you allow yourself to be baited, things may get worse.
After waiting a few hours to respond, you'll be able to focus on the problem or issue that was the origin of the email rather than its tone. Identify an appropriate solution and convey the information to the originator of the rude email.
If you can't solve the problem, tell them so and the reason you can't. If appropriate, tell them you'll convey their concern to the appropriate department or person for handling.
Review the Email Twice, Then Send It
It's best not to transmit an email unless you've had the time to review it carefully first. While some messages contain so few words that it would be difficult to misinterpret their intent, a reader can easily misconstrue a lengthier one. So study the message carefully, particularly if the subject is a delicate one. When you're confident your message is a helpful and amiable one, send it.
Move On to the Next Task
People tend to mull over issues even after they've dealt with them. But there's nothing you can do about a person who chooses to send a rude email. Spare yourself the frustration by issuing your response to the offending message and then moving on to another message or work task. You have more important issues to deal with and more gracious people to help.