Is there a mechanism for verifying an e-mail address exists before sending?
closed as not a real question by pauska, Holocryptic, Iain, mfinni, jscott Aug 16 '11 at 13:40
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RFC 2821's "VRFY" SMTP command is supposed to do that but, due to spammers abusing this command for validating mail addresses lists it's often disabled on the servers and SMTP gateways.