Also mail from mailing lists that you want to receive could be unintentionally deleted. You could filter based on known spammer's e-mail return addresses but they typically use fake addresses and change them frequently. Unfortunately, to date, very few spammers use these tags. Spammers have to obtain your email address from somewhere so the second main approach is to reduce SPAM at its source by reducing the chance that you will appear on a spammer's list. A major source of email addresses is addresses embedded in web pages.
Inexpensive software is available to search the web and extract email addresses.
The customer would need to manually edit the address to reach you. Another possibility is to use a form to allow the customer to submit comments or requests. This method could be instead of or in addition to the disguised email address method. Another source of addresses is return addresses on messages you post to usenet newsgroups. Directories of email addresses such as 411 can also be sources.