550 Requested action not taken: mailbox unavailable

[Teknoratti]

I'm trying to figure out the root cause of an issue we just started receiving from our users from our outlook web stating that emails sent to hotmail / msn emails are getting bounced back with the following: 550 Requested action not taken: mailbox unavailable

According to our users, the email addresses are known good emails, as they can send emails from other emails, i.e, gmail -> hotmail, hotmail -> hotmail, yahoo -> hotmail.

Even if a known good hotmail / msn email is sent to our users and they even try to REPLY to the message that was sent to them it gets bounced back.

Strangely enough it is our internal mail server generating the bounceback with the following:

Generating server: OurMailServer.domain.com

<email name>@hotmail.com
Requested #550 Requested action not taken: mailbox unavailable ##

Original message headers:

Received: from OurMailServer.domain.com ([10.x.x.x]) by
OurMailServer ([10.x.x.x]) with mapi; Wed, 18 Dec 2013 17:40:05 -0500
From: "<name>" <name@domain.org>
To: "<name>" <name@hotmail.com>
Date: Wed, 18 Dec 2013 17:39:56 -0500
Subject: RE: test
Thread-Topic: test
Thread-Index: Ac78QgdKIPlWqboXSNab2Tu5E5166AAAAx3+
Message-ID: <58FA4ACA520A5641941D10DC38408D5C634E08ADDB@ASO00-EXCHBES-1>
References: <BLU180-W31F4AAA25929F173266334DCDA0@phx.gbl>
In-Reply-To: <BLU180-W31F4AAA25929F173266334DCDA0@phx.gbl>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
acceptlanguage: en-US
Content-Type: multipart/alternative;
boundary="_000_58FA4ACA520A5641941D10DC38408D5C634E08ADDBASO00EXCHBES1_"
MIME-Version: 1.0

I've read other forums and researched a bit, some are saying the bounce backs are because the emails are not active and / or the email address doesn't exist, but clearly they are because emails are being sent to us from those addresses, and I even tested with my own personal hotmail accout which I know to be good.

Any help on which way to start my search would be helpful.

 

[Zelandakh]

get-sendconnector | fl
might show you that you have a connector to there. Or a duff DNS entry on that server. The server has been told to deliver emails for those domains to itself hence the 550.

 

[Teknoratti]

@ Zelandakh, The results of the get-sendconnector | fl command is as follows below:

AddressSpaces : {SMTP:*;1}
AuthenticationCredential :
Comment :
ConnectedDomains : {}
ConnectionInactivityTimeOut : 00:10:00
DNSRoutingEnabled : True
DomainSecureEnabled : False
Enabled : True
ForceHELO : False
Fqdn : mail.ourcompany.com
HomeMTA : Microsoft MTA
HomeMtaServerId : Our-Mail-Server-1
Identity : Internet Mail Route
IgnoreSTARTTLS : False
IsScopedConnector : False
IsSmtpConnector : True
LinkedReceiveConnector :
MaxMessageSize : 10MB
Name : Internet Mail Route
Port : 25
ProtocolLoggingLevel : Verbose
RequireTLS : False
SmartHostAuthMechanism : None
SmartHosts : {}
SmartHostsString :
SourceIPAddress : 0.0.0.0
SourceRoutingGroup : Exchange Routing Group <DWBGZMFD01QNBJR>
SourceTransportServers : {Our-Mail-Server-1}
UseExternalDNSServersEnabled : False

I looked at the properties of the send connector for our domain. It uses DNS MX records to route mail automatically. I wondered if our MX records for hotmail are not correct. However, when I ran an nslookup on the MX records for hotmail, they came back correct. We have two DNS servers that I ran the nslookup on. One DNS server came back with MX records for some of hotmails mail servers, the other DNS server returned MX records for the others.

I would think that both DNS servers would be pulling down the same exact MX records for Hotmail.

 

[ShackDaddy]

I think that your server is attempting to connect to the remote servers, but the remote server is rejecting the connection. It is a common problem, and there's not a lot you can do about it, since it has something to do with what the receiving servers think about your sending IP and/or domain name. It could be for all sorts of reasons: IP reputation, IP Subnet reputation, blacklist, RDNS is missing, etc.

Normally what I do is set up an extra send connector just for the problem domains and route those emails through my ISP's smarthost. If you can't use your ISP's smarthost, there are other services (DNSExit, MailHop, etc) that let you relay a small amount of mail through them for a very small fee. That always resolves the issues.

Dave Shackelford
ThirdTier.net

 

[Teknoratti]

@ShackDaddy, thanks for the reply. I initially thought our domain might have been blacklisted, and the results come back ok when I ran our mail server through mxtoolbox.com (mail server blacklist checker).

I will look into your solution to route email destined for hotmail / msn through another smarthost.

 

[Teknoratti]

@ShackDaddy, I guess the issue to get around is how to utilize the third party email relay for ONLY hotmail / msn emails, because again, all our other emails are delivered. We just get bouncebacks from hotmail / msn. As I'm looking at the dnsexit website, I'm wondering if all emails sent would count as using up a relay or if we can specify WHAT email domains we need to be relayed.

 

[ShackDaddy]

It's very easy. Create a new Send Connector. Call it something like "RelayViaDNSExit" and then when it asks you what the address spaces are, put "hotmail.com" and "msn.com".

The default Send Connector has "*" as the address space, so it will be used for all other mail.

Dave Shackelford
ThirdTier.net

 

[Zelandakh]

Yup, that should help.

 

[Teknoratti]

@ShackDaddy, Thanks for your help. I'll test this and let you know. Should be just what I'm looking for.