> WTF, that has been a terrible idea since the 90s, given most spam is > spoofed, the end result of this will be your mail server getting the > poor reputation as source of backscatter and going into blacklists :)
If you reject, you should reject on their SMTP connection. If you return a DSN later, there's a high chance you are causing back-scatter spam to the wrong place. When you reject on the initial connection, if the spammer is abusing someone else's infrastructure, you may cause errors to go back to the owner of that infrastructure which will clue them into a problem they need to clean up. Not always though. Some ESPs track DSNs they get back and remove those addresses from future mailouts. If the spammer reuses that ESP, your address may not be used again with that account. This is really more useful for fringe spam like things you didn't realize you signed up for or things that weren't meant for you. On the other hand, some ESPs let you report the account as spam, but to do that you'd have had to received the message first to click on some link in it. Mailchimp for example lets you click a box to be removed and tell them you consider it spam and if they get sufficient complaints, the account is blocked. In short, I don't think it's bad to reject spam. Care needs to be taken blanket blocking mail from ESPs though.
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