Which sender reputation method works best for you?
Regardless, a good sending reputation means increasing your chances of good deliver- ability — much in the way a person with good credit can score a good deal on a loan increase. In order to manage their customers' sender reputations, many ESPs lump their customers together on a single IP address with a generic domain.
The pros to this method? If you send infrequent volumes you don't have to worry as much about your deliverability, while those with questionable sending reputations can piggyback off the good credit of other pooled ESP customers. The cons? It only takes one or two bad apples to spoil it for everyone else.
If you send significant volume and rely heavily on e-mail, then you should consider switching to a unique IP address and custom DNS. Custom DNS serves as the last link in ensuring your e-mail sending reputation. In fact, not having a custom DNS and a unique IP address means you can't participate in sender verification, white listing and reputation management programs. Also, many corporate phishing filters block links in messages that point to other domains other than the receiving authenticated domain.
So if you send an e-mail from a generic domain and have a link in your message leading to your Web site, it's more likely to get filtered in a corporate network environment. What's a concerned marketer to do? First, get a unique IP address. If your ESP doesn't offer a unique IP address then consider a new ESP. Then, ask your ESP to help you with your custom DNS. They should provide you with a string of DNS entries that include authentication. If you have clean lists and consider branding important, then choose a derivative of your corporate domain name such as e-mail.yourdomain.com. If your list gathering practices are even slightly questionable, then you should purchase a domain specifically for e-mail marketing.
By understanding the status of your reputation, you can figure out which type of method best suits your needs. As a general rule, small infrequent volume works fine for a shared IP address and generic DNS. However, if you plan on dedicating a real budget to the practice, a unique IP address and custom DNS present the best solution.