Most email clients have built in filtering software that blocks emails based on the content in the “from:” and “subject:” lines as well as the body of an email. Filtering software searches for certain keywords and other indicators that identify the email as potential spam. This type of blocking occurs on a per email basis. Sometimes legitimate permission-based email is erroneously blocked due to the limitations of current email filtering software. To avoid your email from being filtered, MyNewsletterBuilder (MNB) recommends avoiding using words like "sale", "limited offer", "discount", as well as using exclamation marks anywhere in the subject line.