两家公司的外部联系人报告说，他们发送给我们的消息返回了以下信息：
451 尝试验证 RCPT 超时[电子邮件保护]对于域名
其中一个公司是一家非常大的国际组织，因此我怀疑问题一定出在他们身上。
我理解此消息通常意味着我的服务器在响应来自另一台服务器的 RCPT 消息之前断开连接。
我有一台 Exchange 2007 服务器，第一个报告该问题的人（以及我能从他们那里获得错误消息副本的人）正在运行 Lotus Domino（我不记得我担任 Domino 支持的日子）。
我们还通过 DNSMadeEasy 使用电子邮件备份服务来处理我们所有的传入消息，以便如果我们的服务器暂时与互联网失去联系，所有消息都会被 DNSMadeEasy 接收和排队，并且在建立连接后，消息将被传递给我们。
我做过的事情：
- 使用我的个人外部帐户测试了内部/外部电子邮件通信，没有任何问题。
- 已验证我没有在 Exchange 中配置反垃圾邮件黑名单。
- 检查了我的 McAfee Groupshield 日志并确认它没有拒绝来自这些发件人的任何消息。
我接下来要去哪里？
以下是 Lotus Notes 针对其认为的问题提供的完整输出（适当隐藏）（抱歉，第一部分的文字太长了，我无法让文字流畅地显示出来）：
> Reporting-MTA: x-local-hostname; localdomain
> Authentication-Results: p01c11m085.mxlogic.net; spf=none X-MXL-Hash:
> 51ae20e2194675c6-9ab61e697b19b6b20a310d95e60b43dac243397d
> From: Mail Delivery System <[email protected]>
> To: [email protected]
> Subject: Warning: could not send message for past 4 hours
> Message-Id: <[email protected]>
> Date: Tue, 04 Jun 2013 11:16:10 -0600
> MIME-Version: 1.0
> X-MX-Bounce: mod_queue/warn
> X-AnalysisOut: [A:9 a=vypMwE87fLIA:10]
> Received-SPF: None
> X-Spam: [F=0.1384615385; B=0.500(0); spf=0.500; STSI=0.500(-49); STSM=0.300(-49); CM=0.500; MH=0.600(2013060409); S=0.200(2010122901); SC=]
> X-MAIL-FROM: <>
> X-SOURCE-IP: [208.65.144.222]
> X-MIMETrack: Itemize by SMTP Server on TheirCompany-NT/TheirCompany(Release 6.5.1|January 21, 2004) at 06/04/2013 12:16:36 PM,
> Serialize by Router on TheirCompany-NT/TheirCompany(Release 6.5.1|January 21, 2004) at 06/04/2013 12:16:38 PM,
> Serialize complete at 06/04/2013 12:16:38 PM
> X-Notes-Item: CN=TheirCompany-NT/O=TheirCompany; type=501; flags=44; name=$UpdatedBy
> X-Notes-Item: 8EC07872:EEDBFA2A-86257B80:005EE789; type=4; name=$Orig X-Notes-Item: ; type=501; name=Categories
> X-Notes-Item: ; type=401; name=$Revisions
> X-Notes-Item: CN=TheirCompany-NT/O=TheirCompany; type=501; flags=0; name=RouteServers
> X-Notes-Item: 04-Jun-2013 12:16:36 CDT/04-Jun-2013 12:16:37 CDT; type=401; flags=0; name=RouteTimes
> X-Notes-Item: 0; name=$MsgTrackFlags
> X-Notes-Item: Tue, 4 Jun 2013 12:16:37 -0500; type=400; name=DeliveredDate
> X-Notes-Item: TheirCompany-NT/TheirCompany!!mail/theirnsf.nsf: =?UTF-8?B?4oChODYyNTcxNUQwMDUzNjc2Nyg=?= =?UTF-8?B?OEVDMDc4NzJFRURCRkEyQTg2MjU3QjgwMDA1RUU3ODkp?=; name=$SJOrigin
> X-Notes-Item: [email protected]; name=$SJInternetAddress
> X-Notes-Item: [email protected]; name=$SJEmail
> X-Notes-Item: p01c11o143.mxlogic.net; name=$SJDomain Received: from p01c11m085.mxlogic.net ([208.65.144.247]) by mail.theirdomain.com (Lotus Domino Release 6.5.1) with SMTP id 2013060412163648-12883 ; Tue, 4 Jun 2013 12:16:36 -0500 Received: from unknown [208.65.144.222] (EHLO p01c11q162.mxlogic.net) by p01c11m085.mxlogic.net(mxl_mta-7.1.0-2) over TLS secured channel with ESMTP id 2e02ea15.0.9233563.00-1301.13111517.p01c11m085.mxlogic.net (envelope-from <>); Tue, 04 Jun 2013 11:16:18 -0600 (MDT) Received: from unknown [10.1.111.143] (EHLO p01c11o143.mxlogic.net) by p01c11q162.mxlogic.net(mxl_mta-7.1.0-3) over TLS secured channel with ESMTP id 2e02ea15.0.9064.00-2396.25366.p01c11q162.mxlogic.net (envelope-from <>); Tue, 04 Jun 2013 11:16:18 -0600 (MDT) Received: FROM queue-bounce BY 01c11o143.mxlogic.net WITH local; Tue, 04 Jun 2013 11:16:10 -0600
> X-Notes-Item: Memo; name=Form
> X-Notes-Item: 1; name=$NoteHasNativeMIME Content-Type: multipart/report; report-type=delivery-status; boundary="Q=_941804289-1370366170-p01c11o143.mxlogic.net"
>
> This is a MIME-formatted message. Portions of this message may be unreadable without a MIME-capable mail program.
>
> --Q=_941804289-1370366170-p01c11o143.mxlogic.net Content-Type: text/plain
>
> ===============================================
> THIS IS A WARNING MESSAGE ONLY
> YOU DO NOT NEED TO RESEND YOUR MESSAGE
> ===============================================
>
> A temporary error occurred while delivering to the following
> address(es):
>
> <[email protected]>: 451 Timeout trying verify RCPT
> ([email protected]) for domain (mydomain.com)
>
> I will continue trying to send the message until it is delivered or
> expires.
>
>
>
> --Q=_941804289-1370366170-p01c11o143.mxlogic.net Content-Type: text/plain
>
> Included is a copy of the message header:
> ----------------------------------------- Received: from unknown [67.89.110.78] (EHLO mail.theirdomain.com)
> by p01c11o143.mxlogic.net(mxl_mta-7.1.0-3)
> with ESMTP id ad5eda15.0.73070.00-330.174376.p01c11o143.mxlogic.net (envelope-from
> <[email protected]>);
> Tue, 04 Jun 2013 07:05:26 -0600 (MDT) X-MXL-Hash: 51ade6163c8c4185-18c8ce3cbb57672918d5c615db6b50a5e7accd4d To:
> [email protected] Subject: Fw: DELIVERY FAILURE: MIME-Version: 1.0
> X-Mailer: Lotus Notes Release 8.5.2 August 10, 2010 Message-ID:
> <OF52E79DBB.50860208-ON86257B80.0047C79E-86257B80.0047D1CD@theirdomain.com>
> From: [email protected] Date: Tue, 4 Jun 2013 08:04:27 -0500
> X-MIMETrack: Serialize by Router on
> TheirCompany-NT/TheirCompany(Release 6.5.1|January 21, 2004) at
> 06/04/2013 08:05:26 AM,
> Serialize complete at 06/04/2013 08:05:26 AM Content-Type: multipart/alternative; boundary="=_alternative
> 0047D1CC86257B80_="
>
> --Q=_941804289-1370366170-p01c11o143.mxlogic.net--