A blacklist is a list of IP addresses or domains that have been identified to have sent spam emails previously. This list is created and gathered by independent spam organizations, and most ISPs and companies would follow such list to filter incoming emails. There are also some companies that have their own internal blacklist system, which blocks emails that they think look spammy.

Getting your emails blocked or landed on the email blacklist has a direct impact on your email deliverability. Here are some best practices that you can follow to avoid your emails from being blocked or blacklisted:

• Ask your recipients to add your email address or domain server/IP into their contact list.

• Send email from a legitimate address that is checked by a real person. Email addresses with random letters and numbers will trigger spam filters and can lead to emails being blocked.

• Clean your email recipient list regularly to avoid repeatedly sending emails to bad or non-existent email addresses.

• Scan your PC with an anti-virus program regularly to ensure it is clean from viruses and malware. An infected PC can be used as part of a botnet to send spam.

• Use strong password for your email account to prevent hackers or other malicious software from compromising your account, sending spams that eventually cause your mail server to be blacklisted. Read more

• Don’t repeatedly send emails with the same or similar content. Every email that you send should consist of unique content.

• Avoid sending attachments. Sending attachments may get your email blocked, but not blacklisted. The effect on deliverability may be the same, but the remedy is to simply not send attachments rather than working to get removed from a list.

• Don’t use punctuation (e.g. exclamation marks) or words that are often used by spammers like “free”, “win”, and “great offer”. Read more

• Check your email content and minimize grammatical mistakes and spelling errors before sending out. Emails with poor spelling and grammatical errors will usually alert spam filters.

• Avoid using too many images in your email. Strive for a healthy balance of images and text to avoid triggering spam filters.

Reference: 15 Do’s and Don’ts to Avoid Having Your Email Blocked or Blacklisted by SparkPost