Hello,

We use our own application to relay our clients email. This application is configured to use the smtp of office365.

All the mails will go from our application, but only the mail who use with the same mail ( 1234@ourenterprise.com) as our office365 account will reach destination.

Do I need to set something in my office365 account, or is that method wrong in itself ?

Thanks for your answers,

Antoine

• Edited by Antoine Menant 21 hours 45 minutes ago

Hi Antoine,

O365 will only allow you to relay email as the registered Accepted Domains only.(Else you might be blacklisting their IPs)

i.e. the sender on the application should be *@ourenterprise.com and not 1234@microsoft.com

SMTP Relay   Any email address (including non-Office365 mailboxes) can send mail using an SMTP relay, as long as it uses a domain thats set up as yours in Office 365.

So if you own @ourenterpriseToo.com, then get it added to the O365 account. Post which it would allow you to relay as that domain as it would be verified and accepted domain for your Office 365 tenant. Else use your on-premises server (But using a domain that you don't own, isn't a very good idea)

TIP: If you have an on-premises SMTP server for example if youre operating in a Hybrid environment then its recommended to use the on-premises server to handle email delivery for applications and devices.

Refer to the below article to find out exact steps required to setup the relay to see if you have missed anything:

How to Allow a Multi-function Device or Application to Send E-mail through Office 365 Using SMTP