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Mailbox Providers and Best Practices

Mailbox Providers and Best Practices

One of the most important parts of getting your email delivered to the inbox is how mailbox providers – like Yahoo! or Gmail – handle the emails being sent through their system. Most use similar rules and best practices for filtering spam emails, though they all put their own twist on delivery. Let’s take a look at some specifics of the big four providers.


Yahoo! filters email based on content and the URLs used in an email. They also filter email addresses by domain, not only IP address. If there’s a domain that has been sending a lot of spam email to their system, Yahoo! will filter them out. Yahoo uses DMARC (Domain-based Message Authentication, Reporting and Conformance), which checks that the sending address matches the From email address. If they don’t match, the email is filtered out. In other words, if you send an email with an From address, you need to be mailing from a Yahoo! account or risk your email going to Spam.


Hotmail (now, uses their own program called SmartScreen to “learn” what junk mail is, and uses old accounts as spam traps. Spam traps, a.k.a. honeypots, are email addresses that aren’t being used, so if emails are sent to these addresses, they can only be spam. Mailing to one of these addresses, even accidentally, can cause serious repercussions, including being banned by an ESP (Email Service Provider). This is why using a double opt-in process is a good idea.


Much like, Gmail collects users’ reports of what is or isn’t spam to filter future emails. Gmail users have the option of clicking a ‘Not spam’ button for any message that’s been accidentally flagged as spam, or, marking anything that goes to the inbox as spam. As long as your Gmail readers don’t consider your email spam, you shouldn’t have inbox delivery problems. Gmail also has two sophisticated inbox filtering options for their users, Folders and Inbox Tabs.


In addition to the best practices we’ve already mentioned, a high number of bounces can harm your email reputation at AOL. You can reduce the number of invalid recipients, or bounces, on your list by using a double/confirmed opt-in. You will always have some bounces due to people changing email addresses, but the lower the number, the better your reputation. Much like Yahoo!, AOL also uses DMARC to authenticate emails being sent to their system.

No matter where in the world you’re sending email, be sure to write content that’s relevant to your readers, keep your list clean by removing bounces and unsubscribes and always follow the requirements laid out by the CAN-SPAM Act.

To learn more check out this post on our Product blog.