Summary
Dealing with IP blocklists, particularly from a major provider like Microsoft, when using a cloud service like Digital Ocean for email sending, presents unique challenges. This is often exacerbated by the nature of shared IP addresses that are common with such providers. Furthermore, the need for email validation, especially for a large customer base, requires careful consideration of methods to avoid further deliverability issues.
Key findings
- Shared IP issues: IP addresses from cloud providers like Digital Ocean are frequently blocklisted by email service providers (ESPs) and mailbox providers (MBPs) due to the activities of other users on those shared IPs. Microsoft is particularly strict with these types of blocklists.
- Provider responsibility: If a block is broad and affects an entire range of Digital Ocean IPs, the responsibility for delisting primarily lies with Digital Ocean. They may need to SWIP (Shared Whois Project) the IP range to the user for better chances of unblocking, but this is often not a simple process.
- SMTP for validation: Using direct SMTP transactions for email validation (pinging mailboxes to check validity) is highly discouraged. This behavior often mimics spammer tactics and will quickly lead to your IPs being blocklisted again by major MBPs, including Microsoft.
- API-based validation: Specialized email validation APIs exist for a reason. They employ more sophisticated and less aggressive methods to check email validity, though the underlying mechanisms of some can still be questionable, involving data purchasing or complex routing.
Key considerations
- Engage Digital Ocean: Contact Digital Ocean's support regarding the blocklist issue. As a user, you may have limited options to directly appeal to Microsoft if the block is against their IP ranges rather than your specific IP reputation. For related issues, see our guide on how to resolve Digital Ocean IP blocks by Outlook.
- Avoid direct SMTP validation: Do not attempt to validate large volumes of email addresses by initiating SMTP transactions from your own IPs, especially if you are on a shared IP pool. This practice will negatively impact your sender reputation and lead to more blocklists.
- Use reputable validation APIs: Opt for a dedicated email validation service via its API, even if it has a cost. The long-term benefits of maintaining good sender reputation and deliverability outweigh the short-term savings of DIY SMTP validation. Mailgun, for instance, offers an email validation API.
- Focus on sender reputation: Understand that IP blocks often stem from broader sender reputation issues. Review your email sending practices and ensure compliance with best practices to prevent future blocklistings. Learn more about why your IP address might be blocklisted.
What email marketers say
Email marketers frequently encounter deliverability challenges when sending from cloud providers like Digital Ocean, largely due to the reputation of shared IP space. The consensus is that direct SMTP validation for a large volume of emails is a risky practice that leads to further blocklisting. Instead, marketers advise leveraging existing email validation APIs or specialized services, despite potential costs, to maintain sender reputation and ensure email deliverability.
Key opinions
- Digital Ocean's reputation: Many marketers acknowledge that Digital Ocean IPs often face deliverability issues because of the significant amount of spam sent by some users on their network, even if Digital Ocean itself has a responsive abuse team.
- SMTP validation risks: Initiating and closing SMTP transactions rapidly for email validation purposes is a known pattern that quickly triggers blocks from major mailbox providers.
- API preference: Email validation APIs are recommended as the standard and safer method for verifying email addresses, as they handle the complexities and risks associated with direct SMTP checks.
- Cost vs. deliverability: While there may be a desire for lower-cost validation methods, the cost of a dedicated validation service is often seen as a necessary investment to protect overall email deliverability and avoid more severe blocklisting issues.
Key considerations
- Assess current sending: If you're already facing blocklisting issues with Digital Ocean, consider if your general email sending practices align with deliverability best practices. Regularly test your email deliverability.
- Leverage existing ESP features: If you're using an ESP like Mailgun, investigate their built-in email validation features, which are designed to handle the complexity without damaging your sending reputation.
- Budget for validation: Allocate budget for a professional email validation service, especially for validating hundreds of thousands of customer emails. This is crucial for long-term email deliverability and avoiding future blocks. The Mailgun blog highlights how to avoid landing on a blocklist.
- Understand blocklist triggers: Be aware that rapid SMTP connections, even if not sending mail, are seen as suspicious by mailbox providers and will lead to swift blocklisting.
Marketer view
Email Marketer from Email Geeks notes that if a block affects a wide range of Digital Ocean IPs, the issue needs to be addressed by Digital Ocean directly. They suggest that only Digital Ocean can effectively communicate with Microsoft to get the IPs unblocked. If users cannot get their IP ranges SWIP'd (transferred) to their own name, it is highly unlikely Microsoft will engage directly with individual customers for unblocking requests. This highlights a critical limitation for those relying on shared IP space from cloud providers.
Marketer view
Email Marketer from Email Geeks advises funneling transactional emails through a reputable service like Postmark. This approach allows users to avoid the complexities and reputation risks associated with managing email sending from self-hosted IPs on cloud providers known for spam issues. It offloads the burden of IP reputation and deliverability management to a specialized provider, which is particularly beneficial for critical communications.
What the experts say
Email deliverability experts highlight that IP blocks from major providers like Microsoft are often a symptom of underlying issues, particularly when using shared IP ranges from cloud hosting providers such as Digital Ocean. They strongly caution against attempting to perform mailbox validation via direct SMTP transactions, as this practice is highly likely to trigger further and more severe blocklistings. Instead, they point to the problematic nature of many email validation services themselves, some of which employ questionable methods, reinforcing the need for caution and reputable partners.
Key opinions
- Digital Ocean's spam problem: Experts agree that Digital Ocean customers, due to the ease of setting up cheap, instant VPSes, contribute significantly to spam volumes, leading to broad IP blocklistings.
- SMTP validation is detrimental: Attempting to unblock IPs for the purpose of direct SMTP mailbox validation will only worsen the situation with mailbox providers, leading to increased scrutiny and tighter blocklists.
- Validation API complexities: The methods used by email validation APIs can be opaque and sometimes problematic, ranging from using botnets and spammer tactics to buying data from ESPs.
- Outsourcing SMTP work: Some validation services maintain their own databases and outsource the actual SMTP validation work to other validators to minimize direct impact on their own IPs, highlighting the sensitivity of this operation.
Key considerations
- Understand underlying causes: Recognize that Digital Ocean IPs may be broadly blocklisted due to historical spam issues from other users. This makes it challenging for legitimate senders to gain trust without specialized intervention. Read our in-depth guide to email blocklists.
- Avoid reputation-damaging practices: Do not pursue direct SMTP verification as a means of email validation, as this is a red flag for MBPs and is likely to result in sustained or new blocklistings. This is a common pitfall that can derail efforts to rehabilitate sender reputation.
- Scrutinize validation providers: Exercise caution when choosing email validation services. Inquire about their methods to ensure they do not engage in practices that could indirectly harm your sending reputation. A discussion on Digital Ocean IPs being blocklisted illustrates these ongoing challenges.
Expert view
Expert from Email Geeks explains that if the block is widespread across Digital Ocean's network, or a broader block than just specific IPs, Digital Ocean themselves are the ones who need to resolve the issue with Microsoft. This is because Microsoft (and other major MBPs) typically only engage with the actual network owner (Digital Ocean) for large-scale delisting requests, not individual customers. The expert implies that individual efforts to delist might be futile in such cases.
Expert view
Expert from Email Geeks adds that if a user cannot get Digital Ocean to SWIP their IP range directly to them, then it's highly unlikely Microsoft will unblock the IPs. SWIP allows the IP user to appear as the legitimate registrant of the IP block, granting them more direct control and legitimacy in delisting requests. Without this, the expert suggests, Microsoft will not consider individual delisting efforts for IPs still registered to Digital Ocean.
What the documentation says
Official documentation from major mailbox providers and email service providers consistently advises against using raw SMTP transactions for email validation, citing it as a practice that harms sender reputation and leads to blocklistings. They advocate for adherence to best practices, including robust email authentication (SPF, DKIM, DMARC), list hygiene, and using their provided APIs for specific functions like email validation. Compliance with their detailed sender requirements is paramount for maintaining deliverability.
Key findings
- SMTP validation policy: Mailbox providers explicitly consider rapid SMTP connections for mailbox validation as suspicious behavior, often resulting in IP blocklistings.
- API recommendation: Major ESPs and MBPs provide their own APIs for email validation, which are the sanctioned and safer methods to check email addresses without risking sender reputation.
- Sender requirements: Microsoft's sender requirements emphasize proper email authentication (SPF, DKIM, DMARC) and maintaining clean mailing lists to ensure messages reach the inbox.
- Proactive measures: A proactive approach to deliverability, including regular audits of authentication records and list cleaning, is critical to avoid blocklists in the first place.
Key considerations
- Adhere to Microsoft's guidelines: For sending to Microsoft domains (Outlook, Hotmail), strictly follow their sender requirements. This includes correctly configuring SPF, DKIM, and DMARC records.
- Utilize validation APIs: When implementing email verification features, prioritize using established email validation APIs. Mailgun's documentation details their email validation API, which is designed for this purpose.
- Maintain list hygiene: Regularly clean your email lists to remove inactive or invalid addresses. This practice reduces bounce rates and spam trap hits, which are common causes for blocklisting.
- Stay updated on requirements: Email service provider requirements evolve. Continuously monitor updates, especially from major players like Microsoft, to ensure ongoing compliance. Review Outlook's new sender requirements for current best practices.
Technical article
Mailgun documentation outlines that their email validation API allows for real-time validation of email addresses using a GET request. This method returns a JSON object containing a `is_valid` boolean, among other details, indicating the validity of the email. This programmatic approach avoids the need for direct SMTP transactions, thereby preserving sender reputation and complying with best practices for email list hygiene. It's designed to be a safe and efficient way to verify email addresses without triggering spam filters or blocklists.
Technical article
Mailgun's guide on Microsoft Outlook sender requirements specifies that senders must start with a deliverability audit to confirm their SPF, DKIM, and DMARC records are correctly implemented and aligned. It stresses the importance of list cleaning to remove invalid or unengaged addresses. These are fundamental steps for any sender aiming to achieve consistent inbox placement with Microsoft domains, as authentication failures and poor list quality are primary causes for filtering and blocklisting.
Related resources
4 resources
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