Summary
The provided answers address the question of which mailbox providers reliably send asynchronous bounces instead of synchronous bounces. The consensus is that no specific provider *reliably* sends async bounces. Bounces are primarily driven by the mailbox provider, not the ESP. Async bounces are increasingly rare due to efforts to combat spam. They are more likely in over-engineered B2B environments or due to temporary email issues. For testing, async bounces can be manually created. Hotmail, via a full OneDrive folder, was suggested as a potential trigger for async bounces. Regardless of the bounce type, managing bounce rates is crucial for maintaining sender reputation and deliverability.
Key findings
- No Reliable Provider: No specific mailbox provider is identified as reliably sending asynchronous bounces.
- MBP Driven: Bounces are primarily driven by the Mailbox Provider (MBP), not the Email Service Provider (ESP).
- Async Rarity: Asynchronous bounces are becoming increasingly rare due to efforts to mitigate backscatter and spam.
- B2B and Temporary Issues: Async bounces are more likely in complex B2B environments or due to temporary email issues (e.g., full mailboxes).
- Manual Creation Possible: Asynchronous bounces can be manually created for testing.
- Hotmail Workaround: Using a full OneDrive folder tied to a Hotmail account may trigger async bounces.
Key considerations
- Sender Reputation: Managing bounce rates is critical for maintaining sender reputation and deliverability.
- Test Before Implement: Testing solutions before implementing on live emails.
What email marketers say
6 marketer opinions
The query asked which mailbox providers reliably send asynchronous bounces instead of synchronous bounces. The responses indicate that while some situations increase the likelihood of asynchronous bounces, no specific provider reliably sends them. Async bounces are more common in over-engineered B2B setups with multiple layers of protection. Temporary issues, such as full mailboxes or server outages, can also trigger async bounces. One suggestion was to use a full OneDrive folder tied to a hotmail account.
Key opinions
- No Reliable Providers: No specific mailbox provider is confirmed to reliably send asynchronous bounces.
- B2B Environments: Over-engineered B2B mailboxes with multiple layers of protection are more likely to generate async bounces.
- Temporary Issues: Temporary email issues like full mailboxes or server outages can lead to async bounces.
- Hotmail workaround: Suggests using a OneDrive folder tied to a Hotmail account may generate async bounces.
Key considerations
- Sender Reputation: Hard bounces, whether synchronous or asynchronous, negatively impact sender reputation, so promptly remove those addresses from your list.
- Bounce Tracking: Implement bounce tracking and categorization to maintain high deliverability and engagement.
Marketer view
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.
20 Mar 2023 - NeilPatel.com
Marketer view
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.
24 Oct 2024 - Email Geeks
What the experts say
5 expert opinions
The responses indicate that mailbox providers, rather than ESPs, primarily drive bounces. Asynchronous bounces are now rare due to efforts to minimize them and prevent backscatter spam. While no mailbox provider reliably sends async bounces, they can be forced for testing purposes. Bounce processing is complex, and identifying specific providers with reliable async bounces isn't straightforward.
Key opinions
- MBP Driven: Bounces are mainly driven by the Mailbox Provider (MBP), not the Email Service Provider (ESP).
- Async Rarity: Asynchronous bounces are rare due to past efforts to mitigate backscatter and spam.
- No Reliable MBPs: No specific mailbox provider reliably sends asynchronous bounces.
- Forced Async: Asynchronous bounces can be forced for testing purposes.
Key considerations
- Bounce Processing: Bounce processing is intricate and dependent on various factors.
Expert view
Expert from Email Geeks explains that bounces tend to be driven by the Mailbox provider and not the ESP.
4 Apr 2022 - Email Geeks
Expert view
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.
14 Dec 2022 - Email Geeks
What the documentation says
3 technical articles
The documentation references outline the technical framework for both synchronous and asynchronous error responses within the SMTP protocol. While SMTP defines both types of responses, and systems like Exchange Online and Postfix generate NDRs, none of the documentation sources specify any mailbox providers that *reliably* send asynchronous bounces. The type of bounce often depends on the nature of the failure and the configuration of the recipient's mail server.
Key findings
- SMTP Definition: SMTP defines both synchronous and asynchronous error responses.
- No Reliable Provider: No specific mailbox provider is identified as reliably sending asynchronous bounces.
- Configuration Dependent: Whether a bounce is synchronous or asynchronous depends on the failure type and the configuration of the recipient's mail server.
Key considerations
- Bounce Processing Tools: Mail transfer agents (like Postfix) offer tools to manage bounce processing according to server responses, but don't guarantee specific async behavior.
Technical article
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.
8 Jan 2023 - Microsoft Learn
Technical article
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.
6 Jul 2021 - Postfix.org
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