Many people do not yet realize that SMTP Virtual server reached the end of support in 2015. But when they migrate to Office 365, they begin to notice that SMTP does not work, and even if it works, tons of problems requiring troubleshooting will arise.

As you already know, SMTP server component feature was built on IIS 6. At this point, you shall relay email to Office 365.

How to set up a multifunction device or application to send email using Microsoft 365 or Office 365 | Microsoft Docs

If you have Exchange On-prem, you can still use your connectors by creating receive connector front-end and adding the serves or clients you need.

The following are links for end of support:

• Internet Information Services (IIS) - Microsoft Lifecycle | Microsoft Docs
• How to: Install and Configure SMTP Virtual Servers in IIS 6.0 | Microsoft Docs
• SMTP relay is unsupported. Article should be updated with a clear statement · Issue #2908 · MicrosoftDocs/OfficeDocs-Exchange · GitHub

The following are tested methods with 2 Products. Every scenario has its own requirements and features. The following table describes all options including Gmail.

Starting with the first tested method

Option 1: Authenticate your device or application directly with a Microsoft 365 or Office 365 mailbox, and send email using:

SMTP AUTH client submission (tested)

This option is very easy, but there’s too many details when configuring a lot of things.

So, the first requirement as per the following note is only authentication. We also have 3 other perquisites.

The following prerequisites is only the authentication requirements

Prerequisites in this note Only

1. No security defaults this can be checked from Azure portal
2. SMTP auth is enabled and this shall be checked from Office 365 portal
3. SMTP AUTH is disabled for any tenants created after January 2020
4. Check SMTP globally and you can enable it per the user

Other prerequisites

Mailbox license, port 587 preferred and DNS use smtp.office365.com

Features

As you can see, you can send in and out and Bypass spam checks

You have lot of homework to do before this method

Script for checking on enabling the authentication per mailbox

• Check SMTP AUTH on all tenant if true then it is disabled if false then it is working (false means working)

• Check SMTP auth for the required mailbox if null then inheriting from tenant and we need to make it false.

#>

Open the Microsoft 365 admin center and go to Users > Active users.

Select the user, and in the flyout that appears, click Mail.

In the Email apps section, click Manage email apps.

Verify the Authenticated SMTP setting: unchecked = disabled, checked = enabled.

When you're finished, click Save changes.#>
get-CASMailbox -Identity "username@domain.com" | Format-List -property smtp*

#Set-CASMailbox -Identity " username@domain.com" -SmtpClientAuthenticationDisabled $false

This means it is disabled for the tenant

Let’s check for the required sender user

null means same as tenant now I will set it to false for this mailbox

Set-CASMailbox -Identity username@domain.com -SmtpClientAuthenticationDisabled $false

Test it on VEEAM

SMTP Settings

SMTP Settings - Veeam Backup for Microsoft Office 365 Guide

Configuring and testing

First method SMTP AUTH client submission.

Second working scenario configure Gmail scenario

Gmail

Received on public emails and Microsoft emails

Appears in the sent items

If you received the following error

Then go to:

https://www.google.com/settings/security/lesssecureapps

make this on

Tested

Appears in sent

We hope we’ve managed to help you out. For more information or if you have any questions, feel free to get in touch with us.

Karim Zaki,

Ctelecoms