Which letter is sent to people to whom shares are not allotted by the company?

Letter of regret

The correct answer is option 3- Letter of regret.

Letter of regret  is sent to people to whom shares are not allotted by the company.

If minimum subscription has been received, the company may proceed for the allotment of shares after fulfilling certain other legal formalities. Letters of allotment are sent to those whom the shares have been allotted, and letters of regret to those to whom no allotment has been made. When allotment is made, it results in a valid contract between the company and the applicants who now became the shareholders of the company.