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IT GuyFlag for United States of America

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Test sending emails to external email address to verify delivery without actually sending email

An important user within my organization received NDRs while replying to emails sent by someone outside of our organization.

We are using Outlook 2016 and Office 365 as our email server.

However, later on the same day, someone else within our organization was able to reply to the exact same emails and these emails reached the person outside of our organization without any problems.

Neither person sending these emails had any attachments sent as part of these email replies.

Since the person we are emailing outside of our organization is a very important person we can't send any test emails or reply to any existing emails to simply test if this issue has been resolved.

So are there any ways we can simulate sending or replying to an email to this person outside of our organization to see if the original issue with the user within my organization had with sending emails to this outside user has been fixed?
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William Fulks
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You could send emails to another address on the same domain, like webmaster@ or something generic they may have setup. Or even get a tech contact there (if they have one) and test with them. That would at least tell you if the problem is domain specific or just account specific.
Did anyone look at the headers of the bounced mail to see why they were bounced?
My solution would be Enable  DKIM and DMARC policies. (they are just a couple of records for dkim and one for dmarc on DNS).
1st Thing...
Enable DKIM for your domain.
Here's a script for that https://gallery.technet.microsoft.com/office/Enable-DKIM-security-on-a151f7c6

Second, Enable DMARC
https://blog.returnpath.com/build-your-dmarc-record-in-15-minutes-v2/

With this, nobody can send an email without being correctly "signed by DKIM" and verified by SPF and DKIM thru DMARC policy.

Jose Ortega
ASKER CERTIFIED SOLUTION
Avatar of Karl Timmermans (Outlook MVP 2012-2018)
Karl Timmermans (Outlook MVP 2012-2018)
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Hi IT Guy,

Assuming that your first user just hit 'reply', and did not alter the recipient's address or anything, and since you had another user (User2) reply to the same email, and it went through, where the first user (User1) replied and it failed, that tells us that there is nothing inherently wrong with your domain or the recipient's domain setup, nor with the recipient as a user.

You don't say whether your first user (User1) has been able to successfully send emails to the other party in the past.  If not, then you should consider checking the setup of your User1, but if they have no problems sending to anyone else, then this is unlikely to be the issue.

Whilst possible that it was a transient issue (at some point we cannot now determine) at the specific time that the email was sent, and if re-sent, it would now be okay.  This is unlikely, since you mention in your post that they received NDRs (plural) in relation to replying to emails (also plural), so they would have to have been phenomenally unlucky to hit transient issues multiple times.

The most likely causes seem to be:

1) There was some word or combination of words in the body of the reply that triggered a filter at the recipient's end (server side or at their client).

2) Your User1 is not permitted to send to the recipient, whereas your User2 is.  This is not uncommon for high profile individuals to have their email setup to only allow specific correspondents who are on their whitelist.


To determine what the actual cause is, whether one of those two or something else, the best place to begin it to examine the original NDRs that your User1 received.  Were they generated by your server, or the recipient's server (or even some other server)?  What precisely did they say?


Alan.