From Green Papers

Participation in Mississippi’s delegate selection process is open to all voters who wish to participate as Republicans. There is no partisan voter registration in Mississippi.

Tuesday 8 March 2016: All 40 of Mississippi’s delegates to the Republican National Convention are allocated to presidential contenders in today’s Mississippi Presidential Primary.

12 district delegates are bound to presidential contenders based on the primary results in each of the 4 congressional districts: each congressional district is assigned 3 National Convention delegates. [Rule 3]
If one candidate receives a majority (more than 50%) of the vote in a Congressional District, that candidate is allocated all 3 delegates.
Otherwise, the candidate receiving the most votes receives 2 delegates and the candidate receiving the second most votes receives 1 delegate.
28 at-large delegates (10 base at-large delegates plus 15 bonus delegates plus 3 RNC delegates) are bound to presidential contenders based on the statewide primary vote. [Rule 4]
Each presidential candidate receiving 15% or more of the statewide vote is proportionally allocated delegates based on their percentage of the vote total of all candidates who met the 15% threshold. Round to the nearest whole number. If no candidate receives 15% of the vote, the threshold is 10%. The process does not describe what to do if too many or too few delegates are allocated due to rounding.
Vote Qual
Vote Del
CD1 3
CD2 3
CD3 3
CD4 3
Statewide 28
Delegates 40
National Convention delegates are bound for the until released by their candidate. [Rules 8 and 9]

In addition, 3 party leaders, the National Committeeman, the National Committeewoman, and the chairman of the Mississippi’s Republican Party, will attend the convention as pledged delegates by virtue of their position. [Rule 5]

Reference: Resolution Of The State Executive Committee Of The Mississippi Republican Party (14 September 2015)