People tell me my Message-IDs are not correct, why aren't they and how to fix it?
The message-ID is a unique identifier for messages you send. To make it unique, Gnus need to know which machine name to put after the "@". If the name of the machine where Gnus is running isn't suitable (it probably isn't at most private machines) you can tell Gnus what to use by saying:
(setq message-user-fqdn "yourmachine.yourdomain.tld")
in ~/.gnus.el. If you use Gnus 5.9 or earlier, you can use this instead (works for newer versions as well):
(with-eval-after-load "message" (let ((fqdn "yourmachine.yourdomain.tld"));; <-- Edit this! (if (boundp 'message-user-fqdn) (setq message-user-fqdn fqdn) (gnus-message 1 "Redefining `message-make-fqdn'.") (defun message-make-fqdn () "Return user's fully qualified domain name." fqdn))))
If you have no idea what to insert for "yourmachine.yourdomain.tld", you've got several choices. You can either ask your provider if he allows you to use something like yourUserName.userfqdn.provider.net, or you can use somethingUnique.yourdomain.tld if you own the domain yourdomain.tld, or you can register at a service which gives private users a FQDN for free.
Finally you can tell Gnus not to generate a Message-ID for News at all (and letting the server do the job) by saying
(setq message-required-news-headers (remove' Message-ID message-required-news-headers))
you can also tell Gnus not to generate Message-IDs for mail by saying
(setq message-required-mail-headers (remove' Message-ID message-required-mail-headers))
, however some mail servers don't generate proper Message-IDs, too, so test if your Mail Server behaves correctly by sending yourself a Mail and looking at the Message-ID.