Use other means to contact buyers and sellers, and avoid the most common cause of negative feedback.
Email is the life's blood of the eBay community. Sellers use it to send payment instructions to buyers, buyers use it to send questions to sellers, and eBay uses it for just about everything.
Unfortunately, there are times when your email never makes it to the other party, either bouncing back or disappearing into the ether. There are two common reasons why your email may never make it to its intended recipient:
The other member's registered email address is out of date. In this case, any emails sent to that address should be bounced back to you. (Note that any user can update their registered email address by going to My eBay Preferences Change my Email Address.)
The other member has an overly aggressive spam filter, which might simply delete all email from unknown addresses (including yours). This means you'll never know if your email made it to the recipient.
Fortunately, there are a bunch of different tools you can use to send a message to another eBay member, useful for when standard email fails:
Contact an eBay Member form. Click any eBay member's user ID to send an email via eBay's mail server. This is useful if you suspect that another member's spam filter is deleting your mail, since it's likely to approve all email originating from eBay.com. However, since it relies on the member's registered email address, it won't help if that address is wrong.
Use a different ISP. If you have an email account with another ISP, try sending your email from there. This will also help get around spam filters. If you don't have another account, you can try getting a free backup address at Yahoo.com or Hotmail.com.
Look in the auction description. If you're a bidder trying to contact a seller, look in the auction description and payment instructions block to see if the seller has specified an alternate email address. Even if you're not bidding on one of their auctions, the seller may have one or more auctions currently running or recently completed that might contain this information.
About Me. If the member's user ID is accompanied by a "me" icon, click the icon to view her About Me page, which might also have alternate contact information. See [Hack #48] for details.
Use your photos. If you're having trouble contacting one of your bidders and you're hosting the auction pictures on your own server, as described in [Hack #59], you can use your photos as another means of communication. Simply add large, extremely clear text to one of your photos instructing the bidder to email you immediately. For best results, increase the canvas size and place red text in the whitespace above the image, which will be more obvious than text placed in the photo.
Dynamic text. Also for sellers: see [Hack #51] for ways to put text in your auctions that can be changed at any time, even after the auction ends. This can be very useful in sending messages to bidders who otherwise cannot be contacted via email.
Send a token payment. If the other user has a PayPal account, try sending a token payment of, say, a single penny, and include your message in the Optional Instructions field. Even if the user doesn't receive payment notification email, the payment will appear the next time she logs into PayPal.
Contact Info. Provided that you and the other member are both involved in a transaction, go to Search Find Members Contact Info, and enter the member's user ID and item number in the spaces provided. eBay will then email both parties with each other's street address and phone number, which you can use as a last resort.
In nearly all cases, one of these methods will get your message across. Make sure that you inform the other person that you have had trouble sending email, and don't be afraid to request that they take steps to rectify the problem. Strangely enough, people are often indifferent to the situation, but suggesting that yours is probably not the only email that isn't getting through is usually enough to convince the recipient to snap into action.
If you're a seller, and your high bidder isn't replying to your emails, you may have a deadbeat bidder on your hands. See [Hack #54] and [Hack #71]for ways to deal with this problem.