smtp relaying


I have a client that uses Office365 for their emails. They have an internet connection through a 3rd party. The users are able to send & receive emails in Office365 without any issues.

However, they have an application which requires details of a SMTP server & authentication to send emails to the other users. We have tried - 587 - TLS to no avail. I cannot use the smtp details of the ISP as we do not have an email account with them to authenticate.

All suggestions are much appreciated. I have tried creating a gmail account & sending emails thru with no success.
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Vasil Michev (MVP)Connect With a Mentor Commented:
There are few ways to use O365 as relay, they are all described here:

In your case, you have most likely tried the "client SMTP subscription" one, which requires a valid Exchange license to be applied to the account you used. And it requires the device to be able to authenticate. Make sure you follow the instructions in the article.
Damien KayConnect With a Mentor Commented:
If all the recipients in the local application are Office 365 users, and you have a static external IP at your Client's  location, then you do not need to use any authentication to use the Relay Options.  Simply choose the options in the first column in the article mentioned above in the first answer.  

Follow the instructions to find the "FQDN of SMTP Endpoint" or "string" for your domain.  It is the same as your MX record, and it should look something like "" It responds on Port 25, without any authentication, as long as the email recipients are using Office 365, and as long as you do not have a dynamic external IP address.

I usually create a CNAME in DNS that points the name "" to the longer name above, as that makes it easier to remember and to use on applications and even "scan to email" devices inside an organization.

If you need to send email via SMTP to users OUTSIDE the O365 organization, then you will need to follow the instructions in the second column, which require a licensed account.
gmail or 365 have to be configured to allow the relaying.  This article should help you through the configuration process:
saliyamAuthor Commented:
Thanks for your advise.
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