When you respond to e-mail, it's helpful to quote relevant passages, so readers get the gist of the discussion. Watch your attributions. Don't omit authors' names in posts you are quoting or mistakenly attribute their comments to someone else. Copyright and libel issues are involved here. Ignore minor errors.
Messages sometimes contain typos, misspellings, Freudian slips, and similar gaffes.
Resist the urge to correct these small mistakes. It wastes time and bandwidth and can result in unproductive flame wars. Avoid personal messages. Use private e-mail instead. Netiquette represents the accumulated social wisdom of the net, the essential protocol for assimilating into the culture of cyberspace.