For me, this forum is about helping and answering questions publicly. I generally only write detailed answers as public messages, so the information stays online and usable for everyone. Well, at least if they can find it among old messages. Google works better than this forum's search.
I have absolutely no intention ever accepting private messages here. The last thing I need is another source of messages that consume my limited time and don't result in building a public knowledge base. This forum software came with tons of unnecessary features. Robin has spent some time turning off lots of the extra junk. It seems private messaging is an integral part of vBulletin.
If anyone knows a way to disable receiving messages on vBulletin, so the sender gets a better error than "inbox full", please let me know. I have a ton of important software work to do, so I just don't have time to fiddle with forum settings.
If you really, absolutely must contact me privately, you can email me directly at paul at pjrc dot com. But please only send email if it's really important and really must be private. Please do not send me technical questions by private email, even if your project is a proprietary project (you can go to a little extra effort to ask with sample code that shows your issue without disclosing your private secrets). Also, understand I am far behind on email and it's very likely I will not reply to your message. I prioritize answering questions publicly on this forum over replying to private email.