We announced at Ignite that we are actively working on bringing dynamic plus aliases to Office 365.
To get around existing usage, the plan is for an opt-in setting. Our ETA is to have this available for all customers by the third quarter of 2020.
I will keep you updated in Uservoice on our progress.Adrian Santangelo commented
Google Apps allows instant creation of an email alias using the "+" feature, for example username+whatever _AT_ domain.com (replace _AT_ with email symbol - don't want to get stuck into a spam filter.) More info here: http://fieldguide.gizmodo.com/how-to-use-the-infinite-number-of-email-addresses-gmail-1609458192
The bigger issue isn't that we can't do that here (as I have users that are quite used to it), but that I can't even CREATE the existing ones. This makes it extremely hard to migration users away from Google Apps since I can't recreate their existing aliases they are already using. Now, I have to have them change every single email address they are using, say to use an underscore instead, then create all of those aliases within the portal. This is an unreal request when trying to sell people on the merits of switching, as the SERVICE is much better, just not the implementation in parts.