My Email is Z80_at_whut.edu.cn(replace the _at_ with @)
When I preview or post,the system always warn about:
The e-mail address entered appears to be invalid. There may be problems with the domain name or with the user mailbox.
Some times, I can ignore it.Other times,I can't.
You are not alone seeing this problem.
I have several times needed to switch between two different email addresses because this site have considered my email address invalid.
I had the same problem when initially downloading the demo version of some of the tools, and since the site caches the result of the mail test, it can take quite a number of times until it considers the email address valid again.
Most probably, the site has a bit too short timeout when checking for an MX entry for the email domain, since it fails while the email address is working and busily receiving mail. When a past has failed because of "invalid" email address, I have immediately checked that the DNS is working as expected, and that it is possible to send mails from sites that shouldn't have any information cached about my email address.