Using subaddress upon reply (supporting subaddressing)

[vltech]

cPanel now supports plus addressing/sub addressing (e.g. "[email protected]") meaning subaddressed email is being delivered correct into IMAP mailboxes, but Roundcube, its default (only?) webmail client, still doesn't support subaddressed email on its end.  It would be great if it did.

One of the main outstanding issues is that when the Roundcube user replies to an incoming subaddressed email, the FROM field of their reply in the Compose pane is not automatically set to the subaddress. Roundcube doesn't detect the subaddress and handle it correctly.

That is, when someone emails "[email protected]", cPanel delivers it correctly to "[email protected]", putting it in the "subaddress" folder.  The Roundcube user sees it as:

From: somebody
To: [email protected]

But when the Roundcube user replies to that email, the Compose pane sets it up:

From: [email protected]
To: somebody

This is incorrect.  To support subaddressing it should be:

From: [email protected]
To: somebody

Right now, the only way for the Roundcube user to get the correct behavior is to manually configure the subaddress as a separate identity and then manually chose it upon reply.  This is not how subaddressing works.  The whole point of subaddressing is that it's supposed to be dynamic and ad hoc. 

The value of subaddressing is that the user should be able to sign up for, say, an email list with the email address "[email protected]" without having to configure that address manually, and when the confirmation email arrives from the list, it is delivered to the "[email protected]" mailbox, into the "listname" folder, which if it doesn't exist is created dynamically (which cPanel all does now), and then when the user replies to that email, the email client (here Roundcube) is supposed to dynamically set the "from" address to "[email protected]", so that the initial sender never receives the email from a different address than the one they sent to.

The whole point of subaddressing is that its a way for users to manage their inbox, avoid spearfishing, and find out which contacts have leaked their contact info.  It doesn't work if the email client doesn't respect the subaddress and exposes the bare address on reply, because further replies from the original sender will just use the bare address, defeating the purpose of having a unique address for each entity one corresponds with.

Similarly, subaddressing doesn't work correctly if the user has to manually configure every sub-address as an identity.  Since subaddressing works by giving unique subaddresses to different organizations, a regular subaddress user can have hundreds or thousands of subaddresses – one for every retailer, social, and online service they use.  That makes manual configuration prohibitive.

A brief discussion of subaddressing is here: https://blog.cpanel.com/plus-addressing-in-cpanel/

I'm not quite sure what the right way to integrate subaddressing into Roundcube would be.  I think it maybe should be an option per each identity that, if turned on for an identity of e.g. "[email protected]", then dynamically handles all the subaddresses.  I don't think anyone wants subaddresses as separate identities in the Identities interface.  Rather, once that option is turned on, the "reply" functionality will dynamically include the right subaddress as the default FROM.

It would also be great if:

• On reply, the UI afforded the user some way of changing to another arbitrary subaddress (i.e. a text input, not a select)
• On compose (originating, not replying) while in a folder not one of the default ones, the UI defaults to the subaddress of the folder.  This could be a property of the folder the user can manually set, but it would be excellent if it could be automatic.