It only occurs when someone has reported your personal message as a spam. Are you advertising via PM or you've been up against someone here in the forum and started to make a war via sending him/her a PM? Someone has probably reported you and it is approved by admin that your PM is a totally spam.

cissrawk is right. It is the only way to unban your account and I'm telling you, there are already some threads/issues about this back in 2017 and having a response to the appeal email really takes some time. And you have a low chance to unban your account unless you have a valid reason.