Clarify single email for MFA (#1984)

### Description

In a [recent internal
discussion](https://elasticco.atlassian.net/browse/IAM-1778?focusedCommentId=251189),
@alxchalkias shared his insights that we could update the doc to make it
more clear that we only support one email factor.

This PR is to address this context piece.

### Preview


[cloud-account/multifactor-authentication.md](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/1984/cloud-account/multifactor-authentication)

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Co-authored-by: Vlada Chirmicci <[email protected]>

Author: kunisen

cloud-account/multifactor-authentication.md

@@ -106,4 +106,12 @@ The only secure and recommended approach is to use one Elastic account for each
 
 For now, you will need to answer an MFA challenge on every login, but we are working on adding a **Trust this device** option, which will "silence" the MFA challenge for one month per user session.
 
+**Can I use multiple email addresses for MFA?**
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+No, only one email address can be used for MFA verification. In alignment with security best practices, Elastic Cloud is designed to use only one designated email address for MFA purposes. This email is used to send your one-time verification codes during login. If you need to update your MFA email address, review [Update your email address](update-your-email-address.md) for more information.
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