A lot of the points on submitting questions also apply to answering questions. Read them.

Has somebody already answered the question? The easiest way to check this is to sort your incoming mail by subject: then (hopefully) you will see the question followed by any answers, all together.

If somebody has already answered it, it does not automatically mean that you should not send another answer. But it makes sense to read all the other answers first.

Do you have something to contribute beyond what has already been said? In general, “Yeah, me too” answers do not help much, although there are exceptions, like when somebody is describing a problem they are having, and they do not know whether it is their fault or whether there is something wrong with the hardware or software. If you do send a “me too” answer, you should also include any further relevant information.

Are you sure you understand the question? Very frequently, the person who asks the question is confused or does not express themselves very well. Even with the best understanding of the system, it is easy to send a reply which does not answer the question. This does not help: you will leave the person who submitted the question more frustrated or confused than ever. If nobody else answers, and you are not too sure either, you can always ask for more information.

Are you sure your answer is correct? If not, wait a day or so. If nobody else comes up with a better answer, you can still reply and say, for example, “I do not know if this is correct, but since nobody else has replied, why don't you try replacing your ATAPI CDROM with a frog?”.

Unless there is a good reason to do otherwise, reply to the sender and to FreeBSD-questions. Many people on the FreeBSD-questions are “lurkers”: they learn by reading messages sent and replied to by others. If you take a message which is of general interest off the list, you are depriving these people of their information. Be careful with group replies; lots of people send messages with hundreds of CCs. If this is the case, be sure to trim the Cc: lines appropriately.

Include relevant text from the original message. Trim it to the minimum, but do not overdo it. It should still be possible for somebody who did not read the original message to understand what you are talking about.

Use some technique to identify which text came from the original message, and which text you add. I personally find that prepending “> ” to the original message works best. Leaving white space after the “> ” and leave empty lines between your text and the original text both make the result more readable.

Put your response in the correct place (after the text to which it replies). It is very difficult to read a thread of responses where each reply comes before the text to which it replies.

Most mailers change the subject line on a reply by prepending a text such as “Re: ”. If your mailer does not do it automatically, you should do it manually.

If the submitter did not abide by format conventions (lines too long, inappropriate subject line), please fix it. In the case of an incorrect subject line (such as “HELP!!??”), change the subject line to (say) “Re: Difficulties with sync PPP (was: HELP!!??)”. That way other people trying to follow the thread will have less difficulty following it.

In such cases, it is appropriate to say what you did and why you did it, but try not to be rude. If you find you can not answer without being rude, do not answer.

If you just want to reply to a message because of its bad format, just reply to the submitter, not to the list. You can just send him this message in reply, if you like.