With the advent of the daily deal e-mail barrage comes the danger of being tossed away as "spam," writes Martin Tobias. Avoid the bigger-is-better mentality by winnowing e-mail lists to loyal and engaged customers. Above all, ensure the content is relevant, substantive and potentially viral. Encourage opting-in by making your subscription box visible and cross-promoted. Provide easy "unsubscribe" features and pay attention to market segmentation.