Most email marketers know that it is important spam-check email messages before sending them out, as this may identify potential issues that cause emails to be marked as spam.It should be noted however that the results generated by the spam-check feature should act as guidelines only. Spam-check is almost always based on the open source software SpamAssassin, whereas large email services employ their own content filters, created internally.There is no magic formula to composing messages that don.