How to send mail over extern SMTP Server from Exchange Online

Question

Hello, I have the following question. We have a mailbox on an external provider's SMTP server (A). Now we want to use M365 mailbox with Exchange Online (B) and send our mails via an email address of the server (A). As if we were sending the mails directly from the server (A). It is important especially because of the SPAM detection at the recipient. I heard that this is possible with transmit connectors. If this works, how do I have to configure the Exchange Server?

Answer 1

Ok, if you want to authenticate directly with Exchange Online, then no connectors are needed. My suggestions are for authenticating with the Server A on-prem and letting it route to Exchange Online.

If you want to connect to directly to Exchange Online with IMAP, that wont work unless your client supports Modern Authentication. Basic Auth is no longer supported in Exchange Online

[https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/deprecation-of-basic-authentication-exchange-online

To Use IMAP, you would need a modern auth IMAP client:

[https://learn.microsoft.com/en-us/exchange/client-developer/legacy-protocols/how-to-authenticate-an-imap-pop-smtp-application-by-using-oauth

TO send via SMTP through Exchange Online, the tenant would need SMTP Auth enabled for your mailbox:

Option 1 sounds like what you need:

[https://learn.microsoft.com/en-us/exchange/mail-flow-best-practices/how-to-set-up-a-multifunction-device-or-application-to-send-email-using-microsoft-365-or-office-365#option-1-authenticate-your-device-or-application-directly-with-a-microsoft-365-or-office-365-mailbox-and-send-mail-using-smtp-auth-client-submission

Answer 2

Are you authenticating to Server A or sending a message through it anonymously?

If authenticating, then you should be good and you just need to connect on port 587 to Server A with the credentials

If sending anonymously through Server A, then a Server A Exchange Admin needs to create an application receive connector that you can relay through anonymously from your own server - scoped to the remote IP range of your sending server.

You can do that following these:

[https://learn.microsoft.com/en-us/exchange/mail-flow/connectors/custom-receive-connectors?view=exchserver-2019#scenario-3-receive-messages-from-a-server-service-or-device-that-doesnt-use-exchange

[https://practical365.com/exchange-2016-smtp-relay-connector/

Answer 3

Hello Andy, we have credentials for an account on Server A. One Username (email) and password. I'm new on Exchange online.

Which kind of connector I have to create on our new M365 Server (B)? In the connector configuration from M365 -> other server I cant define credential for Server A.

And a further question. If it possible to define this configuration for separate e-mail-accounts?

Example with separate credentials?

emailA@serverB.com -> emailA@ServerA.com

emailB@serverB.com -> emailB@ServerB.com

Thanks in advance

Answer 4

Hello Andy, we have credential for account on Server A (username and pass IMAP/SMTP).

I'm new on Exchange online. Which kind of connector I have to create? In der send connector configuration page I cant find the right option where I can define credential for sending mails.

Is it possible to configure this configuration for more than one e-mail-account on one M365 Server?

Example with separat credentials

emailA@ServerB.com -> emailA@ServerA.com

emailB@ServerB.com -> emailB@ServerA.com

Thanks in advance

BR WM

Answer 5

Hi, I probably expressed myself too complex.

We want to use Exchange online as the main system. So when I send a mail from M365 (server B), I want the actual mail to be sent via SMTP server A and not be detected as SPAM by the recipient. on SMTP server B we have a mailbox and the mails should be sent via this.

And the second question would be, is it possible to do it with two mailboxes under one Exchange online M365 account.