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Email deliverability checks to see whether your messages actually reach the inboxes of the people you send them to, or if they end up in spam folders or get blocked by email providers.
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What Is Email Deliverability?
Email deliverability is the ability of your emails to successfully reach the recipient’s inbox, not the spam folder or quarantine.
At its core, deliverability is built on trust. When you send an email, receiving mail servers evaluate whether you’re a legitimate sender or a potential threat. They look at your domain’s authentication (like SPF, DKIM, and DMARC), your sending reputation, and your historical sending behaviour to decide where your message belongs. If that trust is strong, your email lands in the inbox; if not, it may be filtered or blocked.
This process is much more than just delivering. Delivery means that the mail server got your message and didn’t send it back. Deliverability means that the server trusted your message enough to place it in the recipient’s inbox rather than their spam folder. The difference is critical because your security alerts, policy updates, and incident notifications are useless if they don’t get to the right people.
SPF, DKIM, and DMARC are examples of email authentication standards that are the technical basis for deliverability. But reputation is just as important. Internet service providers and email providers keep track of complaints, engagement rates, and sending patterns over time using complex scoring systems.
Sending one campaign to a bad list can hurt your domain’s reputation for months. Deliverability is both a technical problem and a strategic issue for security teams that use email to talk about threats, send out patches, and plan how to respond to incidents.
Why Email Deliverability Matters
Bad email delivery isn’t just a hassle. It’s a business and security risk that makes it harder for you to talk to customers, partners, and employees when it matters most.
According to recent industry data, one in six (roughly 15–20%) of legitimate emails never reach their intended inbox, costing companies valuable time and creating security blind spots when critical alerts go unseen. Links to reset passwords that end up in spam folders cause problems and support tickets. Users are at risk without security notifications. Filters that block invoice emails slow down payments and make it harder to work with vendors.
Problems with deliverability also hurt brand trust in ways that go beyond the inbox. When real emails aren’t consistently reaching their destination, people start to wonder if they can trust each other. They might choose less secure ways to communicate or just stop talking to each other altogether. In the meantime, attackers can use your weakened sender reputation to send phishing emails that look like they come from your domain and are more convincing.
The financial effects add up quickly. Sales teams waste hours following up on emails that no one ever saw. Support teams deal with complaints about messages that were blocked. Marketing campaigns don’t work because they never reach the people they want to. Each blocked email means lost work and missed opportunities.
If your emails don’t get delivered, it could be a sign of bigger problems with your email system or security. If someone hacks into your account and sends spam from your domain, your reputation will suffer. If your authentication protocols aren’t configured correctly, you could be vulnerable to spoofing attacks. To fix deliverability, you need to fix the trust and security issues that caused the problem in the first place.
How Email Deliverability Works
Email deliverability is more like an ongoing test than a simple pass-fail check. Every time you send a message, a complicated series of tests decides whether it goes to the inbox, is filtered to spam, or is completely blocked.
Message Transmission
Your email starts its journey through the infrastructure you use to send it, which could be an internal mail server, a third-party email provider, or a cloud-based email service. The receiving mail server looks at the technical path your message took and checks to see if your infrastructure follows best practices for sending legitimate email.
Authentication Verification
Receiving servers immediately check your authentication protocols. They check SPF records to make sure you’re sending from approved IP addresses, DKIM signatures to make sure the message is intact, and DMARC practices to see how you want messages that aren’t authenticated to be handled. If you don’t pass these checks, you won’t always be rejected right away, but trust is hurt a lot.
Reputation Analysis
Mail providers look at your domain and IP reputation based on data they gather over weeks or months. They look at things like the number of complaints from past recipients, the number of spam trap hits, the number of bounces, and engagement metrics like opens and replies. A good reputation built up over time makes you credible, but a bad one can send even real messages to spam.
Content and Behaviour Evaluation
Filters look for spam signs in the content of your message and also look at how often you send messages. Messages sent to old addresses, sudden volume spikes, or content that looks like known phishing templates are all signs of trouble. Sending messages to engaged recipients in a consistent and predictable way builds trust.
Final Placement Decision
The receiving server weighs all these factors together to make its final decision. High-trust senders land in the inbox automatically. Spam folders or quarantine might hold borderline cases. Messages with the least trust are thrown out before they even get to the recipient.
The Role of Email Authentication
Authentication protocols are the technical foundation of email delivery and the first line of defence against domain abuse. Here are the three main protocols:
- SPF (Sender Policy Framework): This DNS record tells your domain which mail servers and IP addresses are allowed to send email on its behalf. If a receiving server checks your SPF record and finds a match, it means that you’re sending from a real server and not a fake one.
- DKIM (DomainKeys Identified Mail): This cryptographic signature shows that your message hasn’t been changed while it was being sent and that the sending domain really did send the email. Receiving servers use DKIM to tell the difference between real messages and fake ones.
- DMARC (Domain-based Message Authentication, Reporting and Conformance): This policy framework tells receiving servers what to do if SPF or DKIM checks fail. It also lets you see who is sending emails from your domain. DMARC authentication detects unauthorised senders masquerading as your company.
These authentication standards work together to prevent spoofing and protect your brand from email impersonation attacks. They prove your legitimacy to inbox providers, which improves delilverability to your intended recipients. Without proper domain authentication, you risk both delivery failures and security vulnerabilities, which can damage your reputation.
Google and Yahoo Email Authentication Requirements
To protect their users from fake messages and stop the rise of abuse, major inbox providers have raised the bar on email authentication. Google, Yahoo, and Apple made authentication stricter, going from an optional best practice to a required baseline. These changes are part of a larger effort in the industry to cut down on spam, phishing, and domain spoofing attacks that make people less trusting of email.
All senders must follow the rules, but bulk senders who send more than 5,000 messages a day to Gmail or Yahoo accounts have to do even more. All senders must use SPF and DKIM to verify their emails and keep spam complaints below 0.3%. Bulk senders must also post DMARC policies, make sure that their domains are aligned, and include a way for people to unsubscribe with just one click in their promotional messages.
If an organisation doesn’t meet these standards, it will face immediate consequences. As Craig Temple, Sr. Manager of Product Marketing, warns, “If your organisation relies on email to reach customers, non-compliance will directly affect deliverability to Gmail, Yahoo, Apple, and Microsoft users.” Messages from senders who don’t follow the rules may be slowed down, sent to spam folders, or even not delivered at all.
These rules change the way inbox providers check the trustworthiness of senders in a big way. Authentication is no longer a technical nicety that makes it easier to send messages. It decides if your messages will even get through. Companies that treat these requirements as checklists miss the bigger picture: authentication keeps your domain and your ability to communicate safe from threat actors who take advantage of weak email security.
Common Causes of Poor Email Deliverability
Most of the time, bad deliverability doesn’t happen by chance. It usually means that your infrastructure and the inbox providers who are looking at your messages don’t trust each other anymore.
- Missing or misconfigured SPF, DKIM, or DMARC: When core authentication records are missing or broken, inbox providers see a sender who can’t reliably prove who they are. This directly hurts trust and inbox placement.
- Domain spoofing or impersonation: If attackers spoof your domain, providers link that abuse to your brand, which can hurt your reputation and send more of your legitimate traffic to spam.
- Sending from hacked or unauthorised accounts: Hacked users or shadow IT services that send unchecked email act like threat actors, showing that your environment can’t protect its own identities.
- High spam complaint rates: When people keep marking your messages as spam, providers see that as a clear sign that your mail is not only unwanted but also unsafe.
- Bad or getting worse domain reputation: Inbox providers see your domain as a higher-risk sender if it has a history of bounces, low engagement, or risky traffic patterns, even if individual messages look clean.
- Inconsistent or suspicious sending behaviour: Sudden spikes in volume, erratic campaigns, or strange targeting patterns can appear as botnets and phishing operations. This leads to stricter filtering and less trust in the inbox.
FAQs
What affects email deliverability the most?
Email deliverability is most affected by how authentication is set up, how well the sender is known, and how often the recipient opens and reads emails. If your SPF, DKIM, and DMARC records are missing or set up incorrectly, inbox providers won’t trust you. Also, if you send a lot of spam or act badly when you send, your domain’s reputation can be hurt for good.
Is email deliverability a cybersecurity issue?
Yes, email delivery is closely related to cybersecurity. The same authentication methods that help your emails get to the right inbox also keep your domain safe from spoofing and impersonation attacks. When emails don’t get delivered, it often means that there are bigger security issues, like accounts that have been hacked or weak domain protection.
How does DMARC improve email deliverability?
DMARC is built on SPF and DKIM to give inbox providers clear rules on how to deal with messages that say they come from your domain but aren’t authenticated. It shows that you are actively watching over and protecting your email channel, which builds trust and helps legitimate messages get to the top of your inbox.
What happens if an email fails authentication?
Depending on the policies of the receiving provider and the reputation of your domain, messages that don’t pass SPF, DKIM, or DMARC checks may be slowed down, sent to spam folders, or even rejected outright. Repeated failures to authenticate hurt the sender’s reputation and make it harder for even legitimate mail to get through in the future.
Are transactional and marketing emails evaluated differently?
Both transactional and marketing emails go through the same checks for authenticity and reputation. But inbox providers may use different filters based on the content and how people interact with it. Transactional messages, like password resets, usually get more attention, which can help with deliverability, but they still need to be properly authenticated.
Can improving deliverability help reduce phishing and spoofing?
Of course. Strong authentication and DMARC enforcement stop threat actors from spoofing your domain, which keeps your recipients safe and your brand’s reputation high. Better domain protection means that fewer fake messages get through to inboxes, which lowers the amount of abuse that happens with your domain as a whole.
How Proofpoint Helps
Proofpoint’s DMARC authentication and email security solutions help businesses set up strong authentication, keep an eye on domain abuse, and keep the sender trust that inbox providers need. Proofpoint lets security teams protect their domains from spoofing and impersonation while making sure that real messages get to the people they are meant for by combining emerging threat intelligence with authentication management. This all-in-one method sees deliverability for what it really is: a key part of your overall email security. Contact Proofpoint to learn more.
