Online dating etiquette says it's okay to get involved in more conversations at the same time. There is no harm in writing emails back and corresponding with people who contact you. Statistically speaking, one in four or five emails gets an answer. Therefore, you should not write to just one person and just wait for him/her to answer back. The rule works both ways; you don't act against online dating etiquette if you don't answer back to someone who has contacted you.
It is perfectly reasonable to ignore an email if you consider that the sender is not right for you.While in real life such situations are more delicate and usually require an explanation, in the electronic system, you break no online dating etiquette by just turning your back on someone. Plus it would be more offensive to write back and say that you don't find the person suitable. A different issue is when you break up through emails.
Let's say you've met someone online and then went on a real date, but things didn't happen as expected. You can just send that person an email and tell him/her that you would not like to continue seeing each other. However, you would break the online dating etiquette if you met online but went out a couple of times. After several dates, you probably owe the other an explanation. Do it elegantly and in as friendly terms as possible. Plus, you can still continue to write to other people even when dating someone. That is considered acceptable.
It is totally against online dating etiquette to keep your profile up when seriously communicating with someone. Even if the relationship is carried online, there will come a moment when you will meet. You can still continue your online membership and keep your profile, but make sure the profile is no longer active. If you don't follow this very basic guideline you could very well spoil your chance of meeting someone who loves you.
Most of the rules in the online dating ettiquette refer to communication. Rudeness, profanity and dishonesty are beyond acceptance, yet they cannot be eliminated from dating services for good. Well moderated sites are less exposed to rudeness but every online dating web site is exposed to dishonest people.