Make Sure You Get Your Newsletters and Other Good Mail Using Webmail
Gmail: Whitelist a Sender or Domain
Make sure Gmail never thinks messages from certain senders (your friends and family, for example) or domains (say, your company) are spam.
Aliencamel: Whitelist a Domain
If you're getting a newsletter whose address changes from issue to issue you don't want it to look alien to Aliencamel every time. Here's how to whitelist a whole domain in Aliencamel to avoid this problem and a few others.
FastMail: Whitelist a Domain
Protect all mail from a domain from being caught by FastMail's spam filter.
My Way Mail: Make Sure It Never Filters Newsletters as Spam
My Way Mail's spam filters keep your Inbox clean, but they may make a mistake and leave it deserted of your favorite newsletters. Here's how to prevent this by using the "Safe List".
Mailblocks: Make Sure It Doesn't Block Newsletters as Spam
Newsletters often fall victim to a challenge-response technique of preventing spam. Don't let that happen to you and make sure you'll continue to receive your favorite newsletters in Mailblocks.
Windows Live Hotmail: How to Make Sure It Doesn't Ban Important Mail as Junk
Use the "Safe List" in Windows Live Hotmail to make sure mail from people you know or newsletters you have signed up for don't end up in the "Junk" folder.