China has recently blocked all email clients from sending mail. I use Thunderbird for a pop3 account. When I try to send mails, they are blocked and I receive a message stating my mail is spam. If I use the same pop3 account via the state-approved browser site, the mail will go. The block problem occurs for all email clients in the Ubuntu repository [Evolution, Claws, Sylpheed]. I am told Outlook has no such problems. Obviously, China has cut a deal with MS for back doors.

Might anybody know how to work around this to enable T-bird to send emails ?

  • What is your email domain (@xyz.com) and smtp server name?
    – user311189
    Jul 28, 2016 at 0:47
  • @vleague.com.cn smtp.mxhichina.com
    – rob grune
    Jul 28, 2016 at 0:51
  • Set up a VPN to a less restrictive country? Jul 28, 2016 at 0:52
  • @saidakkas: after much research, China seems to use the smtp to detect non-approved email clients and thus block the outgoing emails.
    – rob grune
    Jul 28, 2016 at 0:57
  • If you ping your smtp server, is this the IP you get?
    – user311189
    Jul 28, 2016 at 0:58

2 Answers 2


As per our discussion with @robgrune , his DNS lookups for smtp server is pointing to a different IP address than what global DNS records show.

Finding the correct A record via mxtoolbox for the smtp server and replacing the smtp address with this IP address fixed the issue as a workaround.

However this will cause 'certificate validation errors' if smtp settings include use of encryption. Ideal solution would be to use VPN, then certificate validation failures would not happen and user could be sure that his/her traffic is not intercepted by anyone.



I think that wasn't "Golden Shield Project" that block your e-mail client. Maybe was your e-mail account server that was update, in the server POP3 or IMAP. Try to delete your account of the app and use the automatic function of thunderbird to add the account again. I had the same problem some times ago and I live in Brazil.

Don't forget save the inbox and update your system before to do anything.

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