EmailSenderProvider may take multiple e-mail recipients at once #51244

slothkong · 2026-07-28T13:42:42Z

slothkong
Jul 28, 2026

Current status of this discussion

March 24th, 2026: First discussed with attendees of the KubeCon+CloundNativeCon Europe 2026, one amongst them @slaskawi, who kindly listened to the idea and suggested sharing over here to gather feedback form other maintainers and the wider community.

Problem description

EmailSenderProvider currently accepts only a single recipient address / UserModel. The same is true for the default implementation DefaultEmailSenderProvider. This prevents custom event listeners, authenticators, or admin actions from easily sending out the same single email to a multiple recipients at once.

Picture the following user-story:

WHEN an custom Authentication Flow fires for a new non-admin User
THEN all admin Users (those granted admin Role) within a Realm get notified via email, who can then "reply to all", for example, to acknowledge the incident

To my understanding, devs willing to setup a custom flow to fulfill the story above have gotten only a few incomplete and/or lackluster options:

Loop and send N separate emails: Not particularly scalable, nor fully meeting the acceptance criteria above.

OR

Fully replace the provider: There is evidence that in the past this has been somewhat painful; see for example issues [1][2] around custom EmailSenderProvider in "production mode" or otherwise. I can speak from personal experience an confess I've struggled with this.

OR

Rely on externally-managed email groups: Treating a group email as User email and letting an external SMPT distribute the message to all members of the group is unpractical; maintaining the email group in sync with Keycloak, where the source of truth for who has the admin role is, seems redundant and error-prone. There may be security implications from repurposing a group email as for a User too?

Solution

Add overloaded send methods (or a new method?) that accept a collection of addresses / UserModels (or a richer recipient descriptor). Keep the existing single-recipient methods for compatibility. Document the expected behavior around personalization, BCC/CC and failure handling.

Assumptions

Many extensions can potentially benefit from this; a shared SPI change is cleaner than every plugin re-implementing the sender.
Changes would also include sensible default implementation, i.e. update of DefaultEmailSenderProvider.

P.S.
I have already re-implemented the provider internally. Nevertheless I believe this could bring value upstream and would be willing to open an Issue and a subsequent PR if there is consensus on the API shape. Happy to support with tests and docs as well.

[1] #14522
[2] #23162

cc: @pszabo891, @gudrutis

slaskawi · 2026-08-24T10:19:50Z

slaskawi
Aug 24, 2026

Thanks for writing the proposal up!

Generally, I think it makes sense. Sending an email to multiple Keycloak Administrators will also enable the "reply-all" button, which seems like a nice benefit.

To my understanding, devs willing to setup a custom flow to fulfill the story above have gotten only a few incomplete and/or lackluster options:

Another option worth discussing is extending Kecloak APIs and specific classes to always accept a collection email addresses and rely on one SMTP submission rather than a loop. The implementation should probably aim for backwards compatibility.

0 replies

slothkong · 2026-09-07T20:17:07Z

slothkong
Sep 7, 2026
Author

@stianst, @mposolda, given that you set the foundation on top of which this idea builds, would be amazing to hear your opinion. Would you say this aligns with the scope of DefaultEmailSenderProvider and/or the SPI design philosophy in general?

0 replies

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EmailSenderProvider may take multiple e-mail recipients at once #51244

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EmailSenderProvider may take multiple e-mail recipients at once #51244

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slothkong Jul 28, 2026

Current status of this discussion

Problem description

Solution

Replies: 2 comments

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slaskawi Aug 24, 2026

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slothkong Sep 7, 2026 Author

slothkong
Jul 28, 2026

slaskawi
Aug 24, 2026

slothkong
Sep 7, 2026
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