Jumping up should never be encouraged. It can injure frail visitors and give small children a long-term fear of dogs, not to mention lead to unnecessary laundry bills. All dogs can be trained not to jump up.
If we’re dealing with a mild jumper, talk to visitors about how to greet the dog. Get them to fold their arms, avoid making eye contact, turn around and ignore it. The dog is trying to get attention so if you reward them with attention, you are encouraging the behaviour.
Excessive jumpers require more serious training with definite consequences of action. Ideally have one or two volunteers to help. Get someone to come up to the door, knock or whatever, as if coming through. The instant the dog does one jump, even the smallest jump, get them to silently turn around and walk away. Ideally, they won’t have even made eye contact. They wait, still facing the other way, until the dog has calmed down, then turn around and try again.
This process is repeated until the dog stops jumping. And don’t ever push the dog down, because that’s giving it enough attention to make them do it on the next person. Attention, whether positive or negative, is still attention.