Deliverability issues occur when an ISP throttles, blocks a mailing or sends it to the bulk folder because of too many bad addresses. A poor send will lower your IP reputation and impact your future sends.

Having a recipient opt in is the best way to make sure an e-mail address is valid. There are double opt-ins, active opt-ins and passive opt-ins. The safest method is the double opt-in, in which the recipient receives a confirmation message with an embedded link that must be clicked to validate the address and confirm the desire to receive e-mails.

For active opt-ins, the recipient enters an e-mail address and clicks a box in order to receive mailings. This type of opt-in works best when recipients are instructed to enter the address two times; this reduces “fat finger” mistakes. You end up with more accurate addresses, and recipients are less likely to click on the “this is abuse” button since they actively signed up for the mailing.

Passive opt-ins are those in which the box is already checked when someone visits a Web page or makes a purchase. This is by far the least reliable opt-in method. It generates bad addresses and a high abuse rate.

From a deliverability standpoint, the double opt-in is your best bet, as it validates addresses, reduces abuse complaints and gets mail delivered to recipients that want your e-mail. Your IP reputation is based on delivery rates as well as open rates. The more recipients open your e-mail, the better your IP address looks in the eyes of the ISP.

Robert Consoli is deliverability manager at Silverpop, a provider of e-mail marketing services (www.silverpop.com).