Plus Addressing Now Available in Exchange Online

[The_Exchange_Team]

As announced at Microsoft Ignite 2020, support for plus addressing is now available in Exchange Online. Thanks to our UserVoice site, this feature was identified as the number 1 request for Exchange Admins and we acted on that to bring it to Exchange Online.

Plus addressing allows users to dynamically create unique email addresses that deliver messages to a user’s mailbox, but are easily distinguished from messages sent to the user’s regular email address. There are two main use cases for this. Some customers want to filter incoming email and move certain messages to their own folders. Other customers have business solutions (such as support ticketing systems) that add a case ID to an email address to help track support threads.

Support is currently scoped to mailboxes with support for distribution lists and Groups expected in December 2020.

Plus addressing can be enabled for your organization via PowerShell. The instructions to enable it can be found here.

Additional documentation for the PowerShell command used can be found here.

We really hope you enjoy this new feature we’ve added to Exchange Online, and as always we want to hear your feedback, either here on the blog or over on UserVoice.

Sean Stevenson

Exchange Online Transport Team

[Kam]

Doesn't this mean we can't use + symbols on our email addresses anymore because this is enabled?

[Daniel Niccoli]

That is great news and we're already evaluating to using it in our company.  It would be a great addition if we could change the character from a plus '+' to a custom character, e.g. the underscore '_', because many cloud services and web forms still do not accept the '+'-character as a valid character in an email address.

https://office365.uservoice.com/forums/273493-office-365-admin/suggestions/41763787-allow-custom-cha...

[SyPatWork]

It's a very nice feature, but I can't find the documentation for what will happen with addresses already containing + signs, after turning it on. 

[mri503]

Is sending as a proxy address still in the works?

[stukey]

I can’t see a way to delete or remove a plus address. How do you do that, or is it not possible? Otherwise the usefulness of plus addresses is somewhat limited... you can’t use them as disposable email aliases for specific senders

[Daniel Niccoli]

@stukeyPlus addressing does not offer disposable email addresses, but unique email addresses per recipient (based on the recipient address) that can be created without the hassle of going through IT. You can't delete, remove or disable them. It was never the goal of plus-addresses to offer disposable mail addresses. Your only option is to use rules to delete all incoming mails for specific plus-addresses you handed out.

[ajc196]

EDIT: Got some answers on my own since the feature finally started functioning in our org.

I have a few questions:

1) The detail "Support is currently scoped to mailboxes with support for distribution lists and Groups expected in December 2020" is worded oddly, or maybe by brain isn't functioning today. Just to clarify, this means that Plus Addressing currently works with user mailboxes, shared mailboxes, and resource mailboxes?  And that support for distribution lists and M365 Groups is *not* ready now, but coming in December?

Tests worked to user/shared/resource mailboxes.

2) Is Plus Addressing applicable to any valid SMTP address, or only primary SMTP addresses? (e.g. if my primary SMTP is andrew123@company.com and I have an additional address of andrew345@company.com, then andrew123+newsletters@company.com should obviously work, but would andrew345+newsletters@company.com also work?)

Works for any aliases on a mailbox in my testing.

3) If a mail security appliance (e.g. Cisco CES) does SMTP Call-Ahead to Exchange Online to validate an addresses' existence before delivery, will Exchange Online correctly validate an address using Plus Addressing since it's not an explicit/"real" address on Exchange Online mailboxes?

External messages using Plus Addressing are flowing through our CES appliance fine, so yes, Exchange Online does respond to SMTP Call-Ahead correctly.

4) How long after enabling Plus Addressing with Powershell should it take to function correctly?  I enabled it for my org 2 hours ago, and it is still not even functioning internally. (user mailbox to user mailbox within our own tenant)

It took about 6 hours to finally start working.

[Andres Bohren]

Hi All

In addition to @ajc196 

>How long after enabling Plus Addressing with Powershell should it take to function correctly? 

>I enabled it for my org 2 hours ago, and it is still not even functioning internally. (user mailbox to user mailbox within our own tenant)

I have enabled the Functionality in Powershell 5 Days ago and it still don't work. How long will it take until it's enabled?

Regards

Andres

[Sean_Stevenson]

@ajc196 Thank you for circling back with the answers you found.

Support for Groups and DL is being added and should be available in December. 

@Andres Bohren The time that the setting takes to permeate through the service differs but it should be in the region of hours, not days. If it is still not working, I would advise you to contact support to help diagnose the issue. 

@SyPatWork @Kam We are updating the documentation to be more specific about the expected behaviour. If Exchange Online can resolve the existing address with the plus, then it will be delivered as normal. The problem comes in for mailboxes on-premises that Exchange Online does not know about and message are being blindly routing messages via connector to the mailbox. In such a case, we will assume that the message is a plus address and strip out the plus and tag and deliver it to the parsed address.

@Daniel Niccoli Custom characters for sub-addressing is not something we have any intention to implement in the foreseeable future.

[HotCakeX]

@Kam No, normal free Outlook accounts work fine.

these are applied only to Exchange online.

[Andres Bohren]

Hi All,

@Sean_Stevenson 

I have opened a Microsoft Case.

Result of the MS Case: 

The Option Plus Addressing is not released for Exchange Hybrid Environment. 

Would be nice, if such Informations where already in the initial Blog entry.

As there is a Reference in the Blog to Distribution Groups and Office 365 that they will come later...

Regards

Andres

[Sean_Stevenson]

Hi @Andres Bohren 

Sorry that it wasn't clear. That information about hybrid configurations is in the documentation that is linked to in the blog post:

https://docs.microsoft.com/en-us/exchange/recipients-in-exchange-online/plus-addressing-in-exchange-...

[Andres Bohren]

Hi @Sean_Stevenson 

Thank you for the Link. Can't find "Hybrid" or "Synced" mentioned there.

Tried it for a CloudOnly Account in a Hybrid Environement. Also here Plus addressing to itself (onmicrosoft.com Address) did not work. But that should work right?

[bbzome]

On hybrid environments, mailboxes on-premises can't send emails to "Plus Addressing" mailboxes hosted on Exchange Online with "Recipient not found by SMTP" error.

I expect, at least, that Exchange On-premises knows how to route those messages to Exchange Online.

[benoitrando]

Hello, 

Microsoft announced that the PLUS Addressing will be activated by default to all Tenant .

If I correctly understood, the plus addressing is ONLY working where the MX record or the incoming entry point for email is located in Exchange online . As we still have our MX record located in our on-premise gateway and all incoming emails are still going through our Email gateways, then the PLUS addressing will not work . 

Could you confirm this ?

Thanks

[Sean_Stevenson]

Hi all,

There are many complex routing configurations in our service. We cannot document an exhaustive list of different combinations and how they affect plus addressing. 

The plus addressing functionality exists in EXO and if a message can make it to EXO, it will have the Envelope P1 Recipient stripped of everything after the + thereby allowing it to be delivered with the regular mailbox address after that.

If there is a specific scenario you are not sure about, I encourage you to validate for yourself if and when plus addresses are usable. 

[Andres Bohren]

Hi All,

I've created a PowerShell Script to check for "+" in SMTP Addresses in Exchange Online

https://github.com/BohrenAn/GitHub_PowerShellScripts/blob/main/ExchangeOnline/CheckPlusEmailAddresse... 

Regards

Andres

[Victor Ivanidze]

If you are using plus addressing. have a look at this freeware: https://ivasoft.com/flexaliasesflow.shtml