Answer: The best advice is to start with clean lists and keep them that way. Assuming you (or your e-mail service provider) have the basic technical configurations in place—e.g., RFC-compliant headers and good connections management—the single most important contributor to deliverability is good list hygiene. I think the reason e-mail marketers struggle with list management is because of the inconsistent way marketing departments handle physical addresses versus e-mail addresses.
Because the cost of direct mail is much higher than e-mail marketing, more effort and focus is often placed on scrubbing bad physical addresses from mailing lists. E-mail marketers need to apply that same scrutiny to their e-mail list addresses. While the post office won’t stop delivering your mail because some of your addresses are bad, Internet Service Providers (ISPs) such as AOL, EarthLink or Yahoo! will put a halt to messages from companies that use bad addresses.
In order to keep addresses fresh, send to your lists at least once every 90 days. Any addresses not used for six months have a very high chance of bouncing with sufficient frequency to trip spam filters at some in-box providers. Consider quarantining old addresses from your main list and resoliciting them in small batches using a very "soft sell" designed to minimize complaints.
Another important practice regarding list hygiene is to regularly check your bounce rates. ISPs hate bounced addresses, and they’ll penalize you when you get too many. How many is too many? It depends on the type.
What the industry calls "hard" bounces are typically caused by invalid addresses, and should be removed from lists immediately. "Soft" bounces can be caused by a variety of problems, but often the culprit is an overflowing in-box. Silverpop recommends the "three strikes, you’re out" rule: after three consecutive soft bounces over a greater than 21-day period, addresses should be pulled.
Your goal should be to keep bounces to no more than 4% to 5%. Most companies will find it’s just not cost-effective to try to get below that number. When bounce rates reach 7% or above, caution flags should be raised and the issue should be addressed immediately.
Elaine O’Gorman is VP-strategy for Silverpop, Atlanta.