Which mail box providers reliably send async bounces instead of synchronous bounces?

Email marketer from NeilPatel.com shares that hard bounces (which can be synchronous or asynchronous depending on the specific mail server configuration) negatively impact sender reputation, so it's important to remove those addresses from your list immediately. He doesn't specify which providers reliably use async.

Email marketer from Email Geeks shares that filling a OneDrive folder tied to a mailbox at Hotmail should be a reliable way to generate an async bounce.

Email marketer from Email Geeks explains that async bounces exist mostly in over-engineered B2B mailboxes, where multiple layers of protection can cause bounces at internal SMTP hops due to issues like broken DKIMs and SPFs.

Email marketer from Mailjet shares that temporary issues like full mailboxes or server outages can cause async bounces. Mailjet does not specify any mail box providers.

Email marketer from SparkPost explains that soft bounces (temporary delivery failures) are often delivered asynchronously. The blog does not specify which providers use this format reliably.

Email marketer from SendGrid answers by explaining best practices to track and categorize email bounces to maintain high deliverability and engagement. No mail box providers are mentioned.

Expert from Email Geeks explains that bounces tend to be driven by the Mailbox provider and not the ESP.

Expert from Email Geeks shares that most companies tried very hard to minimize the number of async bounces a while ago due to the backscatter problem and being abused to reflect spam. The cases where async bounces happen now are relatively rare.

Expert from Email Geeks suggests that for testing, you can always force an async bounce by injecting one directly, as the MTA won't know the difference.

Expert from Email Geeks notes that async bounces are very rare, but sometimes unavoidable.

Expert from Word to the Wise explains the intricacies of bounce processing but does not state specific mailbox providers that reliably send asynchronous bounces.

Documentation from Microsoft Learn explains that Exchange Online generates Non-Delivery Reports (NDRs) for failed deliveries. Whether these are synchronous or asynchronous depends on the nature of the failure and the configuration of the recipient's mail server. Microsoft does not explicitly state that Exchange is reliably async.

Documentation from Postfix.org explains that Postfix (a mail transfer agent) handles bounces based on SMTP standards. It doesn't guarantee async bounces from specific providers, but provides tools to manage bounce processing based on server responses.

Documentation from ietf.org explains that SMTP defines both synchronous (occurring during the SMTP transaction) and asynchronous (delayed notification) error responses. While the standard doesn't specify which providers use which method, it outlines the technical framework for both bounce types.