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does the sending email address have a mailbox?
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Yes, and with the vast majority of emails it works. &nbsp;Just this handful of addresses we get a &quot;Accesss Denied&quot; message.
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I see that you're using .net object Mail message.<br />
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Is there a &nbsp;way where the password of those users is wrong?
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Are you able to share if these 4 users reporting the issue have issues only with a Specific Domain or multiple domains that they are sending to?<br />
Are all emails for the domains in question having issues or is the issue random with few emails going through and few failing?<br />
What if any other user than these 4 problem user tries to send email to the same problem email addresses - Do those go through?<br />
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Based on your response we should be able to think of next steps.
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it sound like a SMTP relay problem. please check access settings on you smtp-connector on exchange. there you have to specify, that computer from your local net are allowed to access this server (this seems to be ok) and to relay messages (this is missing).<br />
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Hope that helps<br />
Heiko
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Test each problem email address using <a href="http://www.jetmore.org/john/code/swaks/" rel="ugc"><u>SWAKS</u></a> running through a relay system like MailGun. This will skip over any Office 365 problems.<br />
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If addresses work with SWAKS + MailGun, then you have an Office 365 problem.<br />
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If addresses fail with SWAKS, the recipient addresses are the problem.<br />
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Tip: From the message your posted, it appears the Mailbox you sent to is the problem.
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canuckconsulting

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Sending emails via SMTP using Office 365 resulting in an error of &nbsp;5.4.1 Recipient address rejected: Access denied [BN1BFF011FD005.protection<wbr />.gbl]. &nbsp;This occurs for four of our &gt;&nbsp;100 users and only when sending mail via SMTP. &nbsp;<br />
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<a href="https://filedb.experts-exchange.com/incoming/2019/01_w04/1410045/smtp-error.jpg" target="_blank" title="Error (150 KB)"><img alt="Error" class="file-block lazyload" style="max-width: 800px;" data-src="https://filedb.experts-exchange.com/incoming/2019/01_w04/800_1410045/smtp-error.jpg" /></a>
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smtp-error.jpg

Sending emails via SMTP using Office 365 resulting in an error of  5.4.1 Recipient address rejected: Access denied [BN1BFF011FD005.protection.gbl].  This occurs for four of our > 100 users and only when sending mail via SMTP.  



Sending SMTP email via Office 365 results in error: 5.4.1 Recipient address rejected: Access denied [BN1BFF011FD005.protection.gbl].

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.

Exchange

Office 365 is a group of software plus services subscriptions that provides productivity software and related services to its subscribers. Office 365 allows the use of Microsoft Office apps on Windows and OS X, provides storage space on Microsoft's cloud storage service OneDrive, and grants 60 Skype minutes per month. Office 365 includes e-mail and social networking services through hosted versions of Exchange Server, Skype for Business Server, SharePoint and Office Online, integration with Yammer, as well as access to the Office software. All of Office 365's components can be managed and configured through an online portal; users can be added manually, imported from a CSV file, or Office 365 can be set up for single sign-on with a local Active Directory using Active Directory Federation Services.