[JMAP] Re: JMAP for Calendars comments

[Mauro De Gennaro <[e-mail]>]

1. Yes, in JMAP for Mail a user can create multiple identities and send messages from different email addresses associated with their account. However, Stalwart deliberately restricts what addresses can be added as identities. Users cannot create identities for email addresses or aliases that don’t belong to them. There are a few exceptions: for example, if the added address matches the subaddressing scheme configured by the organization, or if the address is associated with a group the user is a member of. But in general, allowing arbitrary addresses is not permitted to avoid spam, prevent impersonation of other users, and maintain clear ownership of identities.

2. The same principle applies to calendar addresses. Users shouldn’t be able to add ParticipantIdentity objects with calendar addresses that they don’t control or have access to. This is especially important because JMAP for Calendars derives certain access permissions based on these identities. For example, the ability to update RSVP status or to add oneself as a participant. If users could freely add arbitrary calendar addresses, those permission checks could be bypassed or misused.

What I was proposing, for simplicity, is that since the server already knows which calendar addresses a user is allowed to use, we could just expose them directly as part of the Principal object. Similar to how CalDAV handles this with the calendar-user-address-set property. That would make it clearer which identities are valid and avoid potential issues with unauthorized addresses.


Best,
Mauro


> On 5 Oct 2025, at 22:47, Ben Bucksch <[e-mail]> wrote:
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> 
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> Am 5. Oktober 2025 17:30:41 MESZ schrieb Mauro De Gennaro <mauro=[e-mail]>:
>> For example, in Stalwart, calendar addresses are derived from the account’s email address(es) and cannot be modified by users. If we allow users to add other participant identities that are not their email addresses, how should the server validate that they are authorized to use those identities?
> 
> 1. Doesn't JMAP allow for multiple identities and email addresses that are associated with the same mail account? Presumably, if the account has multiple email addresses, then for a reason. Why would an invitation reply be restricted to only 1 of them?
> 
> 2. If the invitation is for a particular email address, the user should be allowed to answer the invitation with the same address, even if it's different from the main email address of the account. Otherwise the user has a problem, because the wrong email address leaks. Or the organizer has a problem, because he gets an answer from an email address that he didn't invite. Or both.
> 
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