Like me, you will find uninvited spam e-mail really irritating. If you are going to trade online, expect a lot more to come your way. Most of it will be adverts, though you will get some email from con artists trying to get hold of your eMail and PayPal account logins.
eBay now has measures to try to reduce spam, though use of e-mail is still an unavoidable part of trading online. When buyers ask you questions via eBay, login to eBay account directly, look for your listing which will show questions against it and answer it from there. Don't respond directly to the e-mail using the "respond" button on your e-mail program. Avoid clicking on the "respond now" button in the e-mail just in case it is a carefully disguised spam e-mail trying to get your account details.
Remember that eBay and PayPal and other reputable online companies will never ask you for your login details directly via e-mail.
Consider using Spam filtering to prevent Spam, most of the latest versions of e-mail software contains some spam filtering.
A secure e-mail solution to consider is Eudora (www.eudora.com). The Lite version is free to download and use.
If the spam gets unbearable, consider changing your e-mail address - there may be a lot of work to change all your account information (in eBay and PayPal etc.) but spammers won't know about your new account for while. If you do this, keep your old e-mail live for a while - in case genuine past customers need to contact you.
Internet Service providers like NTL allow you to setup several e-mail accounts. The accounts in addition to your main e-mail are freely changeable. Setup an additional e-mail account dedicated for use with online trading that is not your main e-mail account.
Also have a look at using free e-mail services: