{"action":"closed","issue":{"url":"https://api.github.com/repos/azumakuniyuki/p5-Sisimai/issues/130","labels_url":"https://api.github.com/repos/azumakuniyuki/p5-Sisimai/issues/130/labels{/name}","comments_url":"https://api.github.com/repos/azumakuniyuki/p5-Sisimai/issues/130/comments","events_url":"https://api.github.com/repos/azumakuniyuki/p5-Sisimai/issues/130/events","html_url":"https://github.com/azumakuniyuki/p5-Sisimai/issues/130","id":118959823,"number":130,"title":"RFC7504 (SMTP 521 and 556 Reply Codes)","user":{"login":"azumakuniyuki","id":194955,"avatar_url":"https://avatars.githubusercontent.com/u/194955?v=3","gravatar_id":"","url":"https://api.github.com/users/azumakuniyuki","html_url":"https://github.com/azumakuniyuki","followers_url":"https://api.github.com/users/azumakuniyuki/followers","following_url":"https://api.github.com/users/azumakuniyuki/following{/other_user}","gists_url":"https://api.github.com/users/azumakuniyuki/gists{/gist_id}","starred_url":"https://api.github.com/users/azumakuniyuki/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/azumakuniyuki/subscriptions","organizations_url":"https://api.github.com/users/azumakuniyuki/orgs","repos_url":"https://api.github.com/users/azumakuniyuki/repos","events_url":"https://api.github.com/users/azumakuniyuki/events{/privacy}","received_events_url":"https://api.github.com/users/azumakuniyuki/received_events","type":"User","site_admin":false},"labels":[{"url":"https://api.github.com/repos/azumakuniyuki/p5-Sisimai/labels/improvement","name":"improvement","color":"207de5"}],"state":"closed","locked":false,"assignee":null,"milestone":{"url":"https://api.github.com/repos/azumakuniyuki/p5-Sisimai/milestones/4","html_url":"https://github.com/azumakuniyuki/p5-Sisimai/milestones/2nd%20Birthday","labels_url":"https://api.github.com/repos/azumakuniyuki/p5-Sisimai/milestones/4/labels","id":1382600,"number":4,"title":"2nd Birthday","description":"","creator":{"login":"azumakuniyuki","id":194955,"avatar_url":"https://avatars.githubusercontent.com/u/194955?v=3","gravatar_id":"","url":"https://api.github.com/users/azumakuniyuki","html_url":"https://github.com/azumakuniyuki","followers_url":"https://api.github.com/users/azumakuniyuki/followers","following_url":"https://api.github.com/users/azumakuniyuki/following{/other_user}","gists_url":"https://api.github.com/users/azumakuniyuki/gists{/gist_id}","starred_url":"https://api.github.com/users/azumakuniyuki/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/azumakuniyuki/subscriptions","organizations_url":"https://api.github.com/users/azumakuniyuki/orgs","repos_url":"https://api.github.com/users/azumakuniyuki/repos","events_url":"https://api.github.com/users/azumakuniyuki/events{/privacy}","received_events_url":"https://api.github.com/users/azumakuniyuki/received_events","type":"User","site_admin":false},"open_issues":5,"closed_issues":9,"state":"open","created_at":"2015-10-29T02:35:47Z","updated_at":"2015-11-29T17:19:23Z","due_on":"2016-08-15T15:00:00Z","closed_at":null},"comments":0,"created_at":"2015-11-26T02:34:30Z","updated_at":"2015-11-29T17:19:23Z","closed_at":"2015-11-29T17:19:23Z","body":"https://tools.ietf.org/html/rfc7504\r\n```\r\n3.  The 521 Reply Code\r\n\r\n   This specification adds the 521 reply code to the repertoire\r\n   specified in SMTP, reserving it for use at connection-opening time to\r\n   indicate that the host does not accept mail under any circumstances.\r\n   It SHOULD be used for dummy SMTP servers whose sole purpose is to\r\n   notify systems that attempt to open mail connections that the host\r\n   never accepts mail.  It MAY be used in other situations where the\r\n   intent is to indicate that the host never accepts mail.  It SHOULD\r\n   NOT be used for situations in which the server rejects mail from\r\n   particular hosts or addresses or in which mail for a particular\r\n   destination host is not accepted.  As discussed in SMTP, reply code\r\n   554 is more appropriate for most of those conditions; an additional\r\n   case, in which the determination that mail is not accepted is\r\n   determined outside the mail system, is covered in the next section\r\n   (Section 4).\r\n\r\n   \"Server does not accept mail\" (or a variant such as \"Host\", \"Domain\",\r\n   or a related term) is an acceptable message to accompany a 521 code\r\n   used for this purpose.\r\n\r\n   Once the 521 reply code is returned instead of the usual 220, the\r\n   SMTP session proceeds normally.  If the SMTP client attempts to send\r\n   additional commands other than QUIT, the server MAY either continue\r\n   sending 521 reply codes or simply close the connection.  If the\r\n   purpose of running a dummy SMTP server that returns a 521 code is to\r\n   conserve resources, the latter will usually be preferable.\r\n\r\n4.  The 556 Reply Code\r\n\r\n   This specification adds the 556 reply code to the repertoire\r\n   specified in SMTP.  When an intermediate SMTP system (typically a\r\n   relay) that would normally attempt to open a mail connection to a\r\n   host referred to in a forward-pointing address can determine that the\r\n   host does not accept mail connections, and do so without attempting\r\n   to open a connection to that target host, it is appropriate for it to\r\n   return a reply with a 556 code to the system that sent it the message\r\n   for outbound transmission.  Interpretation of a special DNS record,\r\n   found when a lookup is performed in conjunction with a RCPT command\r\n   [5], is one such method (and the only standardized one at the time\r\n   this specification was written).\r\n\r\n   When an SMTP server returns a 556 reply code after receiving a\r\n   command (such as RCPT, which contains a forward-pointing address)\r\n   because it has information (such as discussed above) that the mail\r\n   will not be accepted, the SMTP client is expected to handle the\r\n   response like any other permanent negative completion reply to the\r\n   command.  This is consistent with the SMTP specification.\r\n```"}}