How to resolve deliverability issues with .mil email addresses?
Matthew Whittaker
Co-founder & CTO, Suped
Published 7 Jun 2025
Updated 16 Aug 2025
6 min read
Email deliverability to .mil addresses presents unique challenges that differ significantly from standard commercial or even typical government (.gov) domains. I’ve encountered many situations where emails to these accounts are blocked, not due to typical spam flags, but due to the stringent security protocols and network architectures inherent to military systems. These systems are designed with national security in mind, prioritizing controlled access and information integrity over general accessibility.
The U.S. military’s email infrastructure operates under the Department of Defense (DoD) and is often isolated from the public internet or subject to highly restrictive firewalls. This means that traditional deliverability strategies might not apply, and issues can arise from factors like network segmentation, specific content filtering, or even the basic format of your emails.
Understanding these nuances is the first step in resolving deliverability issues. It's not always about improving your sender reputation in the way you would for a standard inbox provider like Outlook or Gmail, but rather adhering to a different set of, often unstated, rules for highly secured environments.
Unique challenges of .mil domains
One of the most common reasons for email blocks to .mil domains is the strict adherence to network and security policies. Unlike commercial internet service providers, military networks are designed to prevent unauthorized access and data breaches. This means that a seemingly benign email from a legitimate sender can still be blocked if it doesn't meet specific, often unpublished, security criteria.
I’ve seen instances where domains were simply pulled out of the public DNS, making them reachable only from specific, internal networks. This isn't a spam-related block, but rather a deliberate compartmentalization of information. In such cases, direct contact with a postmaster or seeking a blocklift through traditional channels may not be effective. The military (DoD) operates under different rules, and their decisions are generally not subject to appeal through commercial means.
A crucial step is to understand if the issue is a genuine block (like being on a blocklist) or if it’s a network-level restriction. For general insights into how to recover email deliverability, you might find this discussion on Reddit helpful, though it applies to commercial scenarios.
Typical email delivery issues
Sender reputation concerns, content flagged as spam, missing authentication (SPF, DKIM, DMARC), high bounce rates, or unsolicited emails.
.mil specific delivery issues
Network isolation, strict internal content filters, plain text requirement, non-commercial use policies, or recipient network access restrictions.
Essential authentication practices
Even with the unique challenges, foundational email authentication remains critical for .mil domains. SPF, DKIM, and DMARC are not just best practices, but often prerequisites for any email to even be considered by these highly secure systems. If your emails lack proper authentication, they will almost certainly be blocked or discarded.
Implementing SPF, DKIM, and DMARC correctly signals to the recipient server that your email is legitimate and hasn't been tampered with. This is even more vital for .mil domains, where security and trust are paramount. A misconfigured record, or a missing one, can lead to immediate rejection.
I always recommend ensuring your DNS records are flawlessly configured for these authentication methods. This is one area where you have direct control over improving your deliverability to sensitive domains. You can refer to our guide on best practices for email deliverability to government and .mil accounts.
Example SPF RecordDNS
v=spf1 include:_spf.example.com -all
Furthermore, consider the implications of being on a public or private blacklist (or blocklist). While .mil domains might use their own internal blocklists, a presence on widely recognized external blacklists can still impact your general sender reputation and, indirectly, their willingness to receive your emails. For more information, read about what happens when your domain is on an email blacklist.
Authentication best practices for .mil
SPF record: Ensure your SPF record correctly lists all authorized sending IPs and domains. Use a hard fail (-all) if possible, after careful testing.
DKIM signatures: Implement robust DKIM signing for all outbound mail. Regular rotation of your DKIM keys is also a good security practice.
DMARC policy: Deploy a DMARC record, even if starting with p=none, to gain visibility into your email streams and identify any authentication failures.
Content, engagement, and alternatives
Beyond technical configurations, the content and format of your emails, as well as how you manage your list, play a significant role. For .mil domains, simplicity and relevance are key. I've found that these domains often prefer plain text emails over rich HTML, as complex formatting can trigger security filters or simply not render correctly.
Ensure your content is concise, directly relevant to the recipient, and avoids anything that could be misinterpreted as commercial or non-official communication. Hyperlinks and images, while standard in marketing emails, should be used very sparingly and only when absolutely necessary for recipients within .mil domains. This is part of a broader set of email deliverability best practices for government domains.
Maintaining a clean and engaged subscriber list is paramount. High bounce rates, even from legitimate addresses that are no longer active, can signal to filters that your list quality is poor. Actively remove invalid or non-existent .mil addresses. For guidance on how email addresses end up on a blocklist, see how your email address ends up on a blacklist.
Email format considerations
Prefer plain text over HTML. Avoid complex layouts, embedded images, and excessive hyperlinks.
Content guidelines
Keep messages concise and directly relevant to military or official business. Commercial content is often blocked.
Finally, if consistent deliverability to .mil addresses is critical for your communication, especially for non-military purposes, encourage your recipients to use an alternative, personal email address. This is often the most reliable path forward, bypassing the strict governmental filters entirely. You can also explore insights on mail deliverability issues for further reading, keeping in mind the specific context of .mil domains.
Views from the trenches
Best practices
Maintain strict email authentication with SPF, DKIM, and DMARC for all sending domains.
Prioritize sending plain text emails to .mil addresses to minimize filtering issues.
Regularly clean your email lists by removing bounced or inactive .mil addresses.
Encourage .mil recipients to use personal email addresses for non-official communications.
Verify the exact nature of blocks, differentiating between spam-related and network access issues.
Common pitfalls
Assuming .mil domains operate like commercial ISPs and apply the same deliverability rules.
Sending HTML emails with complex formatting, images, or numerous links to .mil addresses.
Not maintaining a clean list, leading to high bounce rates from military contacts.
Attempting to appeal blocks through standard postmaster contacts when the issue is network isolation.
Failing to adapt content to be strictly relevant and non-commercial for military recipients.
Expert tips
Consider that .mil domains might have internal DNS setups or be behind firewalls that prevent public access.
Understand that blocklifts are highly unlikely for .mil addresses if the issue relates to their internal security policies.
For non-official communications, direct recipients to use personal email accounts to ensure delivery.
Be aware that military email systems are optimized for official communications, not mass marketing.
Always prioritize security and compliance over marketing aesthetics for .mil communications.
Marketer view
Marketer from Email Geeks says that .mil domains are very special cases, and blocks are often unrelated to typical spam issues.
September 5, 2022 - Email Geeks
Marketer view
Marketer from Email Geeks says that many .mil domains have been pulled out of public DNS and are only reachable from certain networks, meaning they still exist but not publicly.
September 6, 2022 - Email Geeks
Summary
Resolving deliverability issues with .mil email addresses requires a strategic approach that goes beyond typical email marketing best practices. It involves understanding the unique security posture of military networks, ensuring robust authentication, and adapting your content and list management to their specific requirements.
By prioritizing plain text, maintaining impeccable list hygiene, and advocating for personal email addresses where appropriate, you can significantly improve your chances of reaching your intended recipients within these highly secured environments. Always remember that the primary goal of these systems is security, which often supersedes standard email deliverability expectations.
Outlook or 
Gmail, but rather adhering to a different set of, often unstated, rules for highly secured environments.
