Can you configure MS Exchange to support the gmail "+keyword" trick?
It's called "SMTP Tags" or "sub addressing" depending on who you speak to. You may find this wikipedia article useful as it talks about this feature in email.
As a practical matter it isn't supported by quite a few email systems for various reasons - some good (or at least understandable), some not so good. If you use it as an anti-spam mechanism (e.g. to track who gives your address away) then be warned that spammers are smart enough to remove these parts from a list of email addresses...
IIRC, exchange doesn't support it and doesn't really have a mechanism for doing so (you could of course add multiple SMTP addresses to a user's mailbox to create a similar effect but this is obviously very inconvenient to set-up and maintain for all concerned).
This feature is now available on Office 365 Exchange!
Exchange admins will have to enable this manually on their server. This can be done through Powershell using the following command:
Set-OrganizationConfig -AllowPlusAddressInRecipients $true
For instructions on how to use Powershell, you can find out more here: https://docs.microsoft.com/en-us/powershell/exchange/exchange-online-powershell-v2?view=exchange-ps
The setting may not instantly take effect so please expect a delay before you can start using plus addresses.
We're still waiting documentation on this feature and from feedback I've seen, it doesn't work for everyone currently.
TIP: After seeing some feedback, I've done some testing and concluded that this feature may not function correctly on hybrid exchange servers.
Exchange doesn't have the ability to do this. The address is used as a lookup for recipient mail, which is checked against the address lists stored in the system. A new address would have to be added for each tag you use, which is not long term supportable.
However, there are hooks for third party utilities to provide this functionality. The hooks that AntiVirus/AntiSpam systems use, Transport Agents, could be leveraged by such a utility to strip off the information after the + and add it to a mail header, or whatever needs to be done to it. This would allow delivery of the mail to the end user as the To: address would be correctly formatted for Exchange.
I don't know of any packages that do this, though.
I know it's been a long time since originally asked, but this post is still high on Google search results and appears to still be a commonly asked question. So, for those who are curious... although Outlook.com (previously Hotmail) has supported it since 2013, Exchange & O365 doesn't officially support subaddressing per RFC 5233 (at least not as of 2019). However, you may consider the ever fun task of setting up transport rules which allow you to effectively achieve the same thing as described in this blog...
If you want to see it officially supported, you may consider upvoting the request that was started in 2017 to support RFC 5233...