I'm using mailq to monitor my postfix - What do these message codes mean? Is this good or bad?

I am using mailq to monitor my postfix email. I'm getting some emails where there is no readable message that I can understand. It has an email address and then it has characters like this. Do these things have a meaning? What is the meaning? Here are some examples: 368313CCDF* 38551
another one 62EDD3CC5C* 82647
and another one DBD7E3CD1D* 82627