Mailer/daemon..Domain expired..Was their account closed?

I see that some people are having mail troubles lately. I am getting responses to some of my emails, so not sure if I have problem or not. I had a mailer/daemon in my spam today from a mail I sent 3 days ago. Is there anything this could be besides their account was deleted?

Just make sure there your domain company. It could be a trick to steel your domain! That happend to me once. Don't ask me how it went. lol!

It could be a problem with the mail servers you use or they use.

If the server cant find the recipient or the server has corrupt data this could cause the error.

try resending the email again and see what happens, if you can try sending it from another account too like googlemail.