Just saying. Get a decent way to send them, theymos, and send all of them again. You cannot just set up a random server with a random IP address and send mails. It's not the 80's any more. Due to spam epidemic, major mail providers will reject those mails.
The mail certainly came from bitcointalk.org due to the forum's SPF policy, and users have been receiving legitimate mail from bitcointalk.org for years, so any mail provider that bounces forum mail is outright
broken IMO. It's ridiculous that 500,000 users can receive consistent legitimate mail from the forum for years, but then when I want to send them all one mail some of the big providers freak out.