RINSE clean plastic containers and lids with boiling water. Dry thoroughly.
PEEL and pit mangos. Finely chop fruit. Measure exactly 3 cups chopped mangos into large bowl. Stir in sugar. Let stand 10 minutes, stirring occasionally.
MIX pectin and lemon juice. Add to mango mixture; stir 3 minutes or until sugar is dissolved and no longer grainy. (A few sugar crystals may remain.)
FILL all containers immediately to within 1/2 inch of tops. Wipe off top edges of containers; immediately cover with lids. Let stand at room temperature 24 hours. Jam is now ready to use. Store in refrigerator up to 3 weeks or freeze extra containers up to 1 year. Thaw in refrigerator before using.