Well, in the interest of full disclosure...
By default, there is an outbound rate limit of ~50 Mb/sec, mostly to prevent runaway/rogue systems from causing too much damage. At, say, 5 kilobytes per email, that is effectively a rate limit of 1250 emails per second. Also, with a transfer quota of 200 GB/month, you'll start to run into overage fees after ~40,000,000 of these 5 kilobyte hypothetical emails.
Similar mathematics would apply to 5 kilobyte objects via HTTP, 5 kilobyte Usenet articles, 5 kilobytes of pure, uncut Colombian coffee, etc.
Why not rate limit SMTP traffic? If a spam run were to generate abuse complaints at a rate of 0.001%, and were sending out at full speed, a spammer on a Linode should expect to last 40 seconds before an abuse ticket is opened. A spammer using Google Apps at 2,000 e-mails per day should expect to last 25 days. Rate limiting hides the problem;
not rate limiting makes it show up very quickly.
(Note: The math in this speculation, or at least the assumptions, may be dubious. But the point probably isn't.)
This requires that
abuse@linode.com be ruthlessly efficient and empowered to take action. A network's abuse response determines whether or not that network is a spam
haven, which is largely what the reputable DNSBLs consider when deciding to list a network.
If
abuse@linode.com doesn't know who you are, you're not a problem, so why treat you like one?
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