On Tue, Apr 12, 2011 at 2:22 AM, Nathanael C. Cariaga < nccariaga@stluke.com.ph> wrote:
ps. I'm just wondering why yahoo doesn't inform their users that the email that they sent was blocked because of their servers were listed in a blocklist (inspite that the server is able to return a correct reject code 550)
Because 550 is NOT a valid response code at that stage in the conversation. According to the RFC, the only two valid responses to an initial connection are a 220 or a 554. Even then, RFC 2821 doesn't make it clear if a 554 on initial connection should be considered a fatal error at the message level, and as a result most mail servers will consider it a temporary failure and will re-try to send the message multiple times even after getting a 554 (and especially after getting an invalid 550). As someone else has already pointed out, the solution is to return the 5xx response after the rcpt to, not at the initial connection. On 4/12/2011 3:33 PM, Matthew Petach wrote:
-bash-3.2$ telnet qc.stluke.com.ph 25 Trying 219.90.94.56... Connected to qc.stluke.com.ph. Escape character is '^]'. 550 Blacklisted: Blocked - seehttp:// www.spamcop.net/bl.shtml?115.178.12.223
Connection closed by foreign host.
Closing the connection immediately after sending the 5xx is also not RFC compliant. You "MUST" give the client the opportunity to close down the connection with a quit command. Scott