Such notice shall be sent by mail to the taxpayer at the taxpayer's last known address within the time limit provided by § 531 of this title. If the amount of the proposed assessment exceeds the applicable threshold of $1,000, such notice shall be sent by certified or registered mail. . (The applicable threshold in this paragraph is subject to annual adjustment as more fully set forth in § 515 of this title.) In the case of a joint return of personal income tax, a notice of proposed assessment shall be a single joint notice, except that if the Director is notified by either spouse in writing that separate addresses have been established, the Director shall mail a joint notice to each spouse at each such address. In the case of a combined separate return of personal income tax, a single notice of proposed assessment shall be sent by the Director to the taxpayers' last known address except that, if the Director is notified by either spouse in writing that separate addresses have been established, the Director shall mail separate notices to each spouse, using reasonable means to allocate the proposed assessment between the spouses. If the taxpayer is deceased, under a legal disability or is a corporation which has terminated its existence, a notice of proposed assessment shall be mailed to such taxpayer's last known address, except that if the Director has received notice of the existence of a fiduciary relationship with respect to such taxpayer, such notice shall be mailed to the last known address of such fiduciary. Except where the Director determines that collection would be jeopardized by delay, no notice of proposed assessment of any tax shall be mailed prior to the last date, including any date fixed by extension, prescribed for the payment of such tax.
30 Del. C. § 521