Some Exchange 2010 emails not being received by outside recipients

We have Exchange 2010 and are using Outlook 2010 as a client.  Once in a while, when someone here sends an email to multiple recipients the email is not received.  I believe it is only happening when sending to multiple recipients, but I am not 100% sure that it has not occured with just a single recipient.  

I just had an example of this yesterday and today.  A user sent an email to 4 recipients at 4:05pm yesterday and none of them received it.  The same user sent the same email to the 4 same recipients this morning and all of them received it.  I checked with the recipients and yesterday's email was not in their junk or trash folders and they didn't make any changes on their end.  2 are gmail accounts and 2 are other private email accounts.

On our end, the exchange server logs show that it passed the emails onto our GWAVA smtp scanner (GWAVA is an smtp scanner that resides on a linux box and scans our outgoing and incoming email).  I talked to GWAVA support today and they helped me look through the GWAVA smtp logs and it all indicates that nothing was blocked and that it successfully sent the emails out of our system.  

Any ideas as to why it appears that 3 different domains did not receive an email yesterday afternoon but received them today?  I also checked to make sure we are not blacklisted and we are not on any lists that I can find.
PittsfordAsked:
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ArneLoviusCommented:
if the email is passed on to your outbound gateway then the problem is not with exchange.

does your outbound gateway deliver to another smarthost or does it deliver via MX ?

it could be that the recipients of the email have their mail server set to only accept email sent "To:" a single recipient, or have a limit on the number of "CC" recipients.

are you able to reproduce the issue ?

you could tray creating a number of "free" webmail (hotmail, gmail, yahoo mail etc) email accounts for confirming that your outbound gateway is delivering multiple recipient emails correctly.
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BrianRBCommented:
Can the user directly send a message to the recipient and it work fine? Flag the message with a delivery report.  As Arne says, if it gets outside Exchange, it's a problem in an external environment, not yours.
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PittsfordAuthor Commented:
I agree that the issue is not likely an Exchange issue or an issue with our smtp scanner at this point, but I thought I would start with this forum to see if any Exchange admins had any ideas.

Our outbound gateway delivers via MX.

"it could be that the recipients of the email have their mail server set to only accept email sent "To:" a single recipient, or have a limit on the number of "CC" recipients."....I don't think this is it since yesterdays email was exactly the same as todays email and yesterday's didn't work but today's did.  Both emails sent to the same 4 recipients all on the "To:" line and with the same content.

I cannot reproduce the issue myself...a user will report it to me at random times.  I have tried (and just did try a few minutes ago as well) sending a test email to my yahoo, gmail and juno accounts and it went through successfully.  

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BrianRBCommented:
Yeah, the policy for CC/TO is a stretch.  A great point, but I have actually never seen that implemented.  Users would scream!! :)  Watch the queues in real-time and have the user try again. If they send directly to the user, without any other recipients in the message, does the e-mail successfully deliver?
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PittsfordAuthor Commented:
The message that they didn't receive was at 4pm yesterday.  When the sender found out this morning that they didn't receive it, he sent a message to one of the recipients and that person received it.  So he then sent the group email again to the original 4 recipients and it was received this time.

So the tough part of it is they appear to be able to receive messages from us today as a group.  I emailed the 4 of them earlier today and they received my message.  I can send out a new message to the 4 of them and flag the message with a delivery report, but with it working right now, we might not get much info from it.

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BrianRBCommented:
Ah, then do what every great Exchange Admin does.  Point the finger and call it a day. Should it happen again, then call back.  In a few months, it will not matter any way since the world ends right? :)
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PittsfordAuthor Commented:
I actually have been dragging my feet on this one for a few months, but it keeps recurring.  It appears to be a problem that is not going to go away, so I thought I would finally try to get to the root cause of it.  It just doesn't fly with my supervisor for him to send an email at 4pm and come in in the morning and find no one received it.  We don't get any rejection, it's not blocked by anything here and appears to have gone out of here successfully. In lucky cases, the sender finds out that it was not received and then resends it.  In other cases, a different sender has emailed a group of people (a different group) during the day telling them that a meeting has been cancelled that night and then they have all shown up to the meeting because no one in the entire group received the email.  It's just a bizarre thing that it goes out of here completely, never gets received at all at several domains and there's no rejection back to us and no indication it ever happened on the receiving end.  All indicators on our side say it went.  I've tracked email for a long time and have never seen this happen.  I am getting quite a group of people here that have no confidence when they click "send" that it's actually being received on the other side.
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AniDXBCommented:
hi..why dont you send a mail to your personal ID (gmail or yahoo) and view the mail in original source which gives you all the detail of the mail. it can happen if the exchange is not routed through the designated IP.
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JRoyseCommented:
Other domain spam filters may hold an in-rush of mail from one source as suspect, then deliver it later.  Would you say that the TO/CC contents had multiple recipients on the same domain?  Are there large attachments?  Many HTML links?
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PittsfordAuthor Commented:
In response to AniDXB:  I sent an email to one of my home accounts and noticed that there was a message in the header "X-UNTD-SPF: None" and "Received-SPF: None".  So today I added an SPF record to our DNS and now the message in the header is "X-UNTD-SPF: Pass" and "Received-SPF: Pass".  I'm hoping that will help although the recipients have said the emails are not landing in their junk/spam folders.  

It also indicated "DKIM=NONE", but I'm still working on that.  Since all looks well on our servers and it's randomly not getting to the recipients, I'm leaning towards it being DNS-related at this point.

For your comment "It can happen if the exchange is not routed through the designated IP."  Can you expand on that comment so I know what I'm looking for in the headers?
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PittsfordAuthor Commented:
In response to JRoyse:  For the particular email in question there were no attachments and no html links and it was just going to 2 gmail accounts and 2 other private business accounts.
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PittsfordAuthor Commented:
I also just discovered that our smtp scanner for outgoing email did not have our proper host name in the EHLO greeting (exchange's FQDN was ok) .  Just corrected that as well.  Maybe this will help to some degree.
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JRoyseCommented:
I bet the SPF record  is going to help a lot.

Did you use http://mxtoolbox.com/SuperTool.aspx ?
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PittsfordAuthor Commented:
I used www.dnsstuff.com and http://www.allaboutspam.com/

I'll put http://mxtoolbox.com/SuperTool.aspx in my list as well for testing.

I'll keep this issue open a couple days and see if the problem creeps up again.
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AniDXBCommented:
hi.. did you check the IP for the mail server.
Also use this microsoft tool to check your exchange status, will really help you to identify issues and maintain your exchange.

https://www.testexchangeconnectivity.com/Default.aspx
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PittsfordAuthor Commented:
AniDXB: Just used the tool and all looks well with Exchange.  

For your comment "did you check the IP for the mail server"...check it specifically for what?
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AniDXBCommented:
In the test, please check the inbound smtp and outbound smtp tests with your mail server public IP.
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PittsfordAuthor Commented:
I did the test with my mail server public IP for both inbound and outbound smtp and all is well.

I am going to close the ticket since I want to wait until this is reported to me by a user again.  It happens very sporadically so I may have to wait 2-3 weeks...hoping the changes in DNS help esp with the addition of the SPF record.

Thanks for all the suggestions.
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AniDXBCommented:
Thanks !!!
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