Those who reject the Principles of the gospel, including the ordinance of baptism, are damned, not in the “fire and brimstone” sense but rather in the sense that their progression is stopped, their joy is limited because they are not in the celestial kingdom- the only place where there is a “continuation of the seeds forever and ever” (see D&C 132:19-20).
There are varying degrees of damnation just as there are varying degrees or meanings of salvation. In this sense, all who do not attain exaltation are damned, even though they are redeemed and inherit lesser rewards. With the exception of sons of perdition, and subject in many cases to long delays in the spirit prison to allow repentance and reform of those “who shall not be redeemed from the devil until the last resurrection,” all shall ultimately enjoy a glory hereafter which “surpasses all understanding” (see D&C 76:85, 89).