Failure when emailing microsoft 365 accounts from another microsoft 365 account using an alias as the FROM address

Question

Failure when emailing microsoft 365 accounts from another microsoft 365 account using an alias as the FROM address

Graham Smith 5

I have a Microsoft 365 account which has an email alias.

Until earlier this week I could email anybody useing Outlook with the email alias as the FROM address.

Now I can only email people outside the Microsoft cloud. Emailing people with ...@outlook.com addresses give no error but they never receive the email. Emailing ..@gmail.com works normally.

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Answer 1

Alice-N 13,360 Microsoft External Staff Moderator

Hi Graham Smith

I understand that emails sent from your alias are delivered to Gmail, but messages sent to Outlook.com addresses show no error and are not received.

Could you reply with:

Whether the sending account is a personal Outlook.com/Hotmail account or a Microsoft 365 business account.
Whether the primary address delivers to the same Outlook.com recipient.
Whether the alias message appears in Sent Items.
Whether any bounce-back or NDR is received.

Meanwhile, try the checks below:

Send one plain text test email from your primary address to the same Outlook.com recipient. Please do not include a signature, links, images, or attachments.
Then send the same plain text test email from the alias to the same Outlook.com recipient.
Ask the Outlook.com recipient to check the usual locations where messages may be moved or filtered:
- Junk Email
- Other
- Deleted Items
- Any inbox rules or forwarding settings
- If this is a personal Outlook.com alias, verify that the alias is listed under your Microsoft account aliases, then test sending from the alias again.
If Outlook.com recipients still do not receive the alias-sent test messages and there is no bounce-back, please review Microsoft’s sender guidance for Outlook.com delivery issues.

Please tell me how it goes. If the problem persists, please don’t hesitate to reply to this thread and I will be happy to help. Have a lovely day!

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Graham Smith 5 Reputation points

2026-06-28T19:52:20.79+00:00
The account is a personal account.

The primary address delivers corretly to the Outlook.com recipient

I have tried with several different Outlook.com recipients and have the same problem with all of them.

The alias message does appear in Sent items (with a from addres inclusing the on behalf of the primary address.

No bounce or NDR message.

Tried sending test message as suggested. OK when from primary address. No message delivery (but no bounce or NDR) when with alias from address.

Alias listed under the main account. I have even tried deleing it and adding it again verifying address.

This had all been working fine for 9 years!!
Hornblower409 13,825 Reputation points

2026-07-01T04:32:48.1166667+00:00

@Graham Smith said

The alias message does appear in Sent items (with a from addres inclusing the on behalf of the primary address.

Not sure I understand why you are seeing an "on behalf of". Using Outlook Web, when I send from any Microsoft alias for an account it goes out as that alias. No "on behalf of".

Is the alias a non-Microsoft email address? e.g. GMail, Yahoo?
Graham Smith 5 Reputation points

2026-07-01T20:12:01.4666667+00:00

I have been using the classic Outlook on a Windows 11 machine.

I get the "Graham Smith; on behalf of; ******@dunelm.org.uk" if I look in the sent items. (apologies I got it the wrong way round in the description I gave)

The alias is ******@dunelm.org.uk address.
Hornblower409 13,825 Reputation points

2026-07-01T21:32:15.4433333+00:00

@Graham Smith said

I have been using the classic Outlook on a Windows

Thank you for that info. It changes everything. (You tagged your Question as Outlook | Web | Outlook.com )

If you go to https://account.live.com/names/manage is the dunelm domain account listed as an alias for your Microsoft account?
Alice-N 13,360 Reputation points Microsoft External Staff Moderator

2026-07-02T01:14:29.9133333+00:00

Thank you Hornblower409 for the additional steps. Hi Graham Smith, please follow his steps to see if they work, if you encounter any further issues, let me know.

Have a nice day!
Graham Smith 5 Reputation points

2026-07-02T15:41:55.6066667+00:00

Yes. It has been for years. I did try removing it and adding it again in case something had happened.
Graham Smith 5 Reputation points

2026-07-02T15:48:47.44+00:00

In case there was something old with the Outlook classic program I have also tried it with Web Outlook. Same issue.
Hornblower409 13,825 Reputation points

2026-07-02T16:59:59.81+00:00

Graham said > I have also tried it with Web Outlook. Same issue.

I am having trouble reproducing the "on behalf of" process in my environment.

I have a non-Microsoft account (GMail) as an alias for my outlook.com account:

But when I compose a new email in Outlook Web and click the "From" drop-down, the GMail alias is not shown. Only my outlook.com aliases.

1 -- How are you getting Outlook Web to send from your outlook.com account "on behalf of" your dunelm account?

2 -- Is the dunelm account a shared mailbox?
Hornblower409 13,825 Reputation points

2026-07-02T17:21:26.75+00:00

OK. I think I got it. If I manually put the GMail account in the "From" I can get an "on behalf of"

Which shows up at the recipient as

Is this what you see?
Graham Smith 5 Reputation points

2026-07-02T19:01:18.3233333+00:00

Yes that is how I do it and that is what I see for non @outlook.com email addresses.

But if I send to a .....@outlook.com address the email never arrives and no NDR/bounce message.
Hornblower409 13,825 Reputation points

2026-07-02T19:38:35.4866667+00:00

Graham

Thank you for the info. I think the problem is due to the "Unverified" tag.

When you send an unverified email to another outlook.com user it is all handled internally by Microsoft. And, depending on some criteria that I am not privy to, Microsoft might decide to: Send the email to the recipient's Junk folder. Bounce it with a Non-Delivery Report to the sending account (you). Or just silently discard it.

When you send to a GMail user, it is out of Mother Microsoft's hands and GMail will deliver it, if it thinks it's not Spam.

Why did it work in the past?

I can't answer that. Microsoft is constantly changing the rules on what types of unverified emails they will deliver (regardless of the source).

Unless Alice has some other ideas, all I can suggest is that you start a new Question using the "Ask a question" button at the top of this page and ask something like - What determines if an email, from an outlook.com account and flagged by Microsoft as "unverified", is delivered to another outlook.com account or just silently discarded?

Put the URL Link for this thread in the new Question for reference so they will understand the circumstances that are causing the email to be flagged as "unverified".