A mailbox provider is any entity that provides you with an email address. This can be an email provider, such as Outlook, Gmail, Yahoo, and AOL, or an Internet Service Provider (ISP) that also provides a connection to the internet with the email service, such as Comcast or Verizon.
As an Email Service Provider (ESP), getting your email into the inbox is a top priority for us! We think it's important to understand how and why mailbox providers block emails, and what you can do if blocked emails are affecting you:
Why mailbox providers block emails
Mailbox providers use spam-blocking measures to help sort through incoming email and identify the spam to keep their own customers happy; large mailbox providers even boast about being able to keep their users' inboxes "spam-free." Once a mailbox provider identifies a message as unwanted or as spam, they do their best to block all similar messages.
Sometimes these measures can inadvertently block the delivery of legitimate emails because the inbox provider has no way of knowing if the messages were legitimately requested in the first place. When a legitimate email is blocked as spam, it's called a "false positive."
How mailbox providers block emails
Mailbox providers use reputation systems to filter email, drawing in data from many external sources, as well as their own internal data, to determine if your email should be considered spam. Reputation systems are more robust than traditional content filtering and use many data points to score incoming email; traditional content filtering systems often rely on a single bit of content or images.
Of course, all mailbox providers are different, but the following is a list of data points they have available for use in their reputation systems:
- Email content - This includes the subject line, preheader, and body content. The content is scanned for keywords and phrases that trigger spam filtering. You have control over what you put into your email, so make sure to run a spam check before you hit send.
- Images - Images can be scanned for similarity to images that have previously been reported. Emails are also scanned for all-image or image-only content. Make sure your email has some text content to prevent it from triggering a spam filter.
- URL block lists - If a URL in your email is listed on a block list, it can get your email blocked as spam. There are several public block lists that are designed to prevent access to malicious content; mailbox providers can also compile their own block list. Linking only to URLs for reputable web pages within your emails can prevent blocks.
- Source IP for your email - When you send mail through Constant Contact, it’s sent through our mail servers and, therefore, is associated with our IP address. We work hard to protect our reputation as an email sender and actively monitor accounts to prevent spam activity. We’ve also built relationships with many mailbox providers so that we can act quickly to resolve issues associated with our IP address if they arise.
- Individual recipient preferences - This is based on what your contact chooses in their inbox settings. It can be anything from having your "From Email" address added to their safe-sender list, or having your email filtered to a specific folder or tab.
- Individual recipient actions - Many mailbox providers manage base email reputation on the behavior of their customers. For example, if a user never opens your emails, the next one you send could be automatically filtered into the spam folder in favor of emails from senders that get opened and read more often, or if a user marks your mail as spam, it's possible that future mail with similar content could also be blocked. If you notice a contact is frequently listed as “did not open” in your reporting, it may be time to rethink how frequently you send them emails, figure out what content truly engages them, or remove them from your list altogether.
- Individual past spam treatment - If an individual has marked your email as spam in the past, it's likely to be treated as spam going forward, even if the individual has signed up for your email list.
- Content association - There could be nothing wrong with your email, but your message could look similar to a completely unrelated message that the recipient has marked as spam in the past.
What to do when a mailbox provider blocks your emails
If you do discover that your Constant Contact email is being blocked, a good first step is to look at the prior engagement of the blocked address or addresses. If the contact was:
- Previously opening your emails - It's likely something may have changed with the content of the email or the sending address, and you should contact our Support Team to help you troubleshoot the blocking. Having specific examples of contacts who were previously engaged prior to bouncing is useful prior to calling Support.
- Never opening your emails - It's likely a problem with list hygiene. Removing disengaged contacts and keeping a clean list of engaged contacts helps to reduce blocks and improve your open rate.
We work with many mailbox providers and corporate mail administrators to successfully resolve issues with blocked emails. Once we have the opportunity to explain our business, they're willing to work with us to resolve the issue. We also speak with any larger mailbox provider that isn't currently accepting email from Constant Contact. For smaller mailbox providers and domains, we've found that when they hear from their own users who want to receive our email, it usually yields faster results, so we've created some form letters to help you communicate with the mailbox provider directly.