Summary
When transactional emails sent from a WordPress site via Mailgun encounter rate limiting from Outlook and Yahoo, it often points to a complex interplay of factors beyond simple volume, including IP and domain reputation, email authentication, and the specific sending behavior of the WordPress setup. Even with a reputable service like Mailgun, a new sending stream or inherited poor domain reputation can trigger ISP filters. This situation highlights the importance of understanding how major mailbox providers assess inbound mail, especially for critical transactional messages like password resets or account validations.
Key findings
- Rate limiting indicators: Outlook's S775 error and Yahoo's TSS04 message both signal temporary rate limiting due to IP reputation, unexpected volume, or user complaints.
- Shared ip implications: For low-volume senders, using a shared IP (common with Mailgun for small sites) means your deliverability is influenced by the collective sending behavior of other users on that IP pool.
- Domain reputation inheritance: If emails were previously sent directly from a WordPress site on a hosting provider with a poor reputation (like OVH, often associated with spam), your domain's negative history can carry over, impacting deliverability even after switching to a better ESP.
- Authentication alignment: Ensuring proper SPF, DKIM, and DMARC alignment is fundamental, but even with correct setup, other factors can cause issues.
- Warm-up period: A new mail stream from Mailgun, even if the domain is old, needs a warm-up period for ISPs to build trust and stabilize sending reputation.
Key considerations
- Monitor and wait: For newly configured sending, allow several days for ISP filters to adapt and for the shared IP reputation to stabilize. If deferrals persist after a week, further investigation is warranted.
- Check wordpress security: WordPress sites are often targeted by bots for subscription bomb attacks. Implement CAPTCHAs and closely monitor new sign-ups or email triggers to prevent unsolicited emails from damaging your sending reputation. For more details, see our guide on why your transactional emails go to spam.
- Contact mailgun support: Verify if you are on a shared or dedicated IP and inquire about their IP pool behavior and any guidance they can provide on your specific rate limiting issues.
- Review postmaster tools: Regularly check Outlook Postmaster and Yahoo Postmaster for insights into your sending reputation and specific error codes.
- Understand deferrals: While annoying for transactional emails (e.g., password resets), deferrals are temporary and usually result in eventual delivery, unlike rejections. This is covered more in our guide on rate limiting due to IP reputation with Microsoft.
What email marketers say
Email marketers often face immediate and practical challenges when their transactional emails are rate limited, especially when moving from a basic hosting setup to a specialized Email Service Provider (ESP) like Mailgun. Their focus is typically on restoring timely delivery for critical messages like welcome emails and password resets. The frustration stems from seemingly well-configured systems still encountering blocks, leading to questions about IP types, sending volume, and the impact of past sending history. Marketers often seek quick solutions and clear guidance on how to navigate these technical issues without deep deliverability expertise.
Key opinions
- Immediate impact: Rate limiting on transactional emails (like forgotten passwords) creates significant user experience issues due to prolonged delivery times.
- Shared ip concerns: There's common confusion about whether using a shared IP from an ESP like Mailgun is the cause of rate limiting, particularly for very low sending volumes.
- Authentication validation: Even after confirming that SPF, DKIM, and DMARC authentication appears aligned, marketers still struggle to pinpoint the root cause of deliverability issues.
- Plugin reliability: Some marketers find that WordPress SMTP plugins provide a clear view of triggered emails, helping them confirm legitimate sending activity on their end.
Key considerations
- Diagnosing unknown history: When inheriting a project with existing deliverability problems and limited historical data, the initial focus should be on establishing a clean sending path and monitoring results before deep diving into legacy issues. Refer to our article on Outlook deliverability issues.
- Trusting the ESP: For low-volume senders, an ESP like Mailgun is generally the recommended solution over self-hosting, as they manage IP reputation and infrastructure complexities. You can also review our guide on transactional email deliverability.
- Patience with new setups: Even if the domain has historical issues, a new sending configuration through a reputable ESP needs time to build a fresh reputation with ISPs.
Marketer view
Email marketer from Email Geeks shared that they had set up a Mailgun account for a client's existing domain to resolve email deliverability issues, specifically for transactional emails from a WordPress site using the WP Mail SMTP plugin, which worked fine for Gmail but resulted in rate limiting for Outlook and Yahoo recipients.
Marketer view
An email marketer from Email Geeks noted that Outlook's feedback in Mailgun's admin, indicating a temporary rate limit due to IP reputation, was a key issue, alongside a similar message for Yahoo recipients regarding temporary deferrals due to unexpected volume or user complaints.
What the experts say
Deliverability experts underscore that shared IP rate limiting for low volumes often signals underlying issues beyond the IP itself, such as domain reputation or message content. They highlight the persistent challenges of WordPress as a sending platform due to its vulnerability to abuse and its default lack of proper authentication, which often necessitates an ESP. While ESPs generally offer better deliverability, experts also recognize that previous bad domain reputation can hinder new setups and that a warm-up period is critical for establishing trust with ISPs. They emphasize the need to look at the broader sending ecosystem rather than solely focusing on IP addresses.
Key opinions
- Shared ip nuances: Low-volume sending on a dedicated IP can struggle to build reputation, while shared IPs might face issues from other senders in the pool. Neither is inherently good or bad; it depends on volume and pool quality.
- Domain reputation is key: IP reputation is less of a concern than domain reputation, particularly if Mailgun's shared IPs generally have decent standing.
- WordPress vulnerabilities: WordPress is notoriously susceptible to abusive bots that can trigger unsolicited emails, potentially harming sender reputation through unwanted volume or complaints. This means you need to be familiar with WordPress email issues.
- Warm-up essential: Even with an ESP, a new mail stream needs time to warm up and build trust with ISP filters, especially if the domain was previously sending from a compromised or low-reputation source like a generic PHP host.
- Deferrals are temporary: A 4xx deferral means the email is temporarily held but will likely be delivered eventually, contrasting with rejections. However, these delays are unacceptable for transactional emails.
Key considerations
- Authentication check: Verify SPF, DKIM, and DMARC alignment using tools like AboutMy.Email to ensure foundational authentication is solid. You can learn more about SPF, DKIM, and DMARC in our comprehensive guide.
- Historical reputation: If the domain previously had very poor deliverability (e.g., sending from an OVH VPS), Mailgun's service needs time to overcome that inherited negative perception. This relates to understanding your email domain reputation.
- Content and engagement: Even with technical fixes, consistent good sending practices, including relevant content and positive user engagement, are crucial for long-term reputation building and avoiding blocklists.
- No self-hosting for low volume: For small volumes (dozens of emails/day), running a dedicated mail transfer agent (MTA) like Postfix or Kumo is overkill and not truly free due to maintenance and infrastructure costs.
- Patience is key: Often, allowing a new Mailgun setup a few days to settle can resolve temporary rate limiting without complex interventions.
Expert view
Expert from Email Geeks stated that hiding the IP address in a query makes it extremely difficult to provide effective assistance for deliverability issues.
Expert view
An expert from SpamResource comments that a temporary IP block often means that the mail will be delivered eventually, or it'll escalate to a rejection, so if rejections are not being seen, the only issue is delayed sending.
What the documentation says
Official documentation from major mailbox providers like Outlook (Microsoft) and Yahoo (Oath) consistently points to IP and domain reputation as critical factors in email delivery, including rate limiting. These platforms often issue temporary deferrals (4xx errors) when they detect unusual sending patterns, poor sender history, or lack of proper authentication. Their guidelines emphasize the importance of adhering to best practices such as robust authentication (SPF, DKIM, DMARC), maintaining a clean sending list, and avoiding sudden spikes in volume. Mailgun's own documentation on bulk sender changes for Google and Yahoo further reinforces these requirements, particularly DMARC alignment.
Key findings
- Explicit rate limit errors: Microsoft's S775 error code (4.7.650 The mail server [...] has been temporarily rate limited due to IP reputation) and Yahoo's TSS04 error (Messages from [...] temporarily deferred due to unexpected volume or user complaints) clearly state the reasons for deferral.
- Reputation-based filtering: Both Outlook and Yahoo use sender IP and domain reputation as primary signals for filtering, including the application of rate limits and blacklisting.
- Authentication requirements: Recent bulk sender changes by Google and Yahoo, as detailed by Mailgun, emphasize strong email authentication (SPF, DKIM, DMARC) as a prerequisite for good deliverability and avoiding rate limits.
- Volume consistency: Unexpected spikes in sending volume or a lack of consistent volume for new IPs can trigger rate limiting, as ISPs aim to prevent abuse and manage their network load.
Key considerations
- Postmaster tools utilization: Leverage official postmaster tools (Outlook, Yahoo) to gain insight into your sender reputation, email volume, and specific error codes, which are crucial for diagnostics. We have an ultimate guide to Google Postmaster Tools.
- DMARC alignment for compliance: Mailgun's FAQ specifically mentions DMARC alignment (e.g., 4.7.32 This mail has been rate limited because there is no DMARC alignment) as a reason for rate limiting, indicating it's a critical compliance factor.
- Address underlying complaints: Yahoo's TSS04 error explicitly mentions user complaints as a reason for deferral, underscoring the need to ensure recipients genuinely want your mail.
- IP reputation requests: Microsoft's support page at olcsupport.office.com provides a pathway to request IP reputation review, although it's often a secondary step after internal troubleshooting and warm-up.
Technical article
Documentation from Mailgun states that the error code 4.7.32 This mail has been rate limited because there is no DMARC alignment is a specific reason for rate limiting related to Google and Yahoo's bulk sender policy changes, indicating the necessity of DMARC alignment for reliable delivery.
Technical article
Documentation from Outlook Postmaster indicates that a mail server can be temporarily rate limited due to IP reputation, as evidenced by the S775 error code, urging senders to consult their postmaster site for delivery information.
Related resources
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Related pages
Why are my emails having deliverability issues with Microsoft Outlook and Hotmail?
What causes severe email rate limiting at Oath (Yahoo) and how can senders recover?
Why do emails sent through SendGrid go to spam on Outlook.com, but those from O365 do not?
What causes temporary rate limiting due to IP reputation with Microsoft email servers?
Why is my email getting throttled by Gmail and Microsoft despite high engagement and good reputation?
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