In a wide bowl, crush strawberries in batches until you have 4 cups of mashed berries.
In a heavy bottomed saucepan, mix together the strawberries, sugar, and lemon juice. Stir over low heat until the sugar is dissolved.
Increase heat to high, and bring the mixture to a full rolling boil. Boil, stirring often, until the mixture reaches 220 degrees.
Transfer to hot sterile jars, leaving 1/4 to 1/2 inch headspace, wipe rim and seal. Process in a water bath. I pour in a bit of vinegar to the water bath so the jars do not have that filmy residue. If the jam is going to be eaten right away, don't bother with processing, and just refrigerate.
Process in boiling water bath for 15 mins. Remove and do not dry tops. Let air dry and make sure they seal. Remove rings before storing.