Now formula:
DATETIME_FORMAT(NOW(), 'M/D/YYYY')
Due in 1 day formula:
IF(
{Due Date} = "",
"Unsure of due date",
IF(
DATETIME_FORMAT({Due Date}, 'MM/DD') = DATETIME_FORMAT(DATEADD(NOW(), 1, 'day'), 'MM/DD'),
"TRUE",
"No match"
)
)
Change the "1" to however many days in advance you want your email to come through