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Prevent emails from being blocked

You may find out from subscribers, or by sending test emails, that your emails are being sent to the junk or spam folder, instead of the inbox. Below, we'll explain the most common causes for this, and give you some advice on what to do.

Unauthenticated email

Depending on how an inbound email server is configured, it will use various methods to determine whether an email comes from:

  • the server it claims it is from

  • the email address it claims it is from

  • a server that has been authorized to send on behalf of that email address.

To address this, don't send from a free webmail address and, if you haven't already, authenticate your sending domain.

Spammy content

The content of your email can result in an inbound email server sending it to the spam folder. Spam filters look at an email as a whole, with thresholds set for certain criteria. If a threshold is exceeded, the email gets marked as spam.

Things that can be caught by spam filters can include:

  • An entire email composed of capital letters

  • Frequent, random capitalization

  • Excessive punctuation, especially "$" and "!"

  • Strange spacing or excessive amounts of blank space

  • Poor spelling

  • Frequent variations in text color and size

  • Scam-like subject lines

Emails that contain unbelievable claims about earning money fast, free products/services, adult content, gambling, prizes and pharmaceuticals are also high risk for being marked as spam, and are all prohibited by our anti-spam policy.

Blocks by ISPs

ISPs consider every spam complaint an official complaint from their customers. This means that if enough recipients mark your email as spam, the ISP may respond by blocking future emails from you.

We also monitor spam complaints made against every email you send. If complaints for a single email exceed industry thresholds — anything above 0.1% — your account could be suspended.

Custom spam filters

Most major email providers (for example AOL, Hotmail, Yahoo and Gmail) use "smart" filters to detect unwanted email, meaning the filter rules change based on past emails, who sent them, and how the recipient interacted with them. Different recipients can have different filters, and because of this your email may land in the inbox of one subscriber, but in the spam folder of another.

Additional spam filters or rules may have been set up by a company's IT department, or by individual recipients. For example, a person who has decided they want to unclutter their work email inbox could set up a filter to send any email that has the word "sale" in it to their spam folder.

One way to address this is to ask your subscribers to add your email address or domain to their safe sender lists (Outlook 2003–2016), address books (Apple Mail, Mozilla Thunderbird) or contacts (Gmail, Yahoo,, AOL, iOS). Usually the best time to do this is in your introductory email.

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