Unfortunately, no e-mail marketing software is certified ‘un-spammable’. There are things you can do, however, to reduce the likelihood of a message being marked as spam.
Common problems occur in the subject line of the e-mail. A subject that is too long or has multiple punctuation marks (i.e. exclamation points, question marks, quotations, etc...) used together can cause your message to appear as spam to many mail box filters.
To help determine whether you message is likely to be marked as spam or not, use the spam tool in the EMS. This tool is a link located on the last page before you hit ‘send’ to start your e-mail blast, and offers a ‘spam rating’ for your message. Try using this on future e-mails to determine their likelihood of being marked as spam.
You might also want to research some effective e-mail marketing writing methods to improve the success rate of future e-mails. Here’s a helpful resource for writing e-mail subject lines.