Email Undeliverable? Here Are 6 Main Reasons Why
Email delivery issues can disrupt communication and, surprisingly, aren’t uncommon. Whether it’s a simple typo, a full inbox, or a technical glitch, understanding the root causes can help you take action. This guide breaks down the six most common reasons why emails fail to deliver and offers practical solutions to ensure your messages reach their destination every time.
Every email you send has a purpose. Whether you’re reaching out to a client, sharing exciting news, or confirming plans, it’s frustrating when that crucial message doesn’t reach its destination.
If you’ve ever stared at a bounce-back email wondering, What happened? — you’re not alone. Email deliverability issues can happen to anyone, but the good news is that most have clear explanations—and fixes.
Here’s a look at the six most common reasons emails go undelivered and what you can do to ensure your messages land where they belong: in the recipient’s inbox.
The #1 reason for email undeliverable is an incorrect email address
It happens to the best of us — you hit “send” only to realize the email address had a typo or wasn’t updated. Whether it’s an extra letter, a missing dot, or a completely outdated domain, even small mistakes can prevent your message’s delivery.
The good news? This is one of the easiest issues to prevent. Here are some quick checks to keep your emails on the right path:
- Double-check before sending. Take a moment to verify the email address, especially if you’re typing it manually or copying it from another source.
- Use an email checker if it’s your first time using that email. You should have an email verification service that allows you to check email addresses quickly. Never send an email to test if it works.
Pro-tip: If you send an email just to test if the email is still working, you may get a bounce. Getting bounces causes your sender reputation to suffer and will prevent future emails from landing in the inbox, even to people you regularly communicate with.
Ways to avoid having an incorrect email address
- Keep your contact list updated. If you regularly email the same people or keep an email list, you should clean up your contact database periodically. Remove inactive addresses or update any that have changed.
- Use autocomplete with caution. Autocomplete is convenient, but it can also pull in old or incorrect addresses. So always double-check before selecting it. Remove an email address once you’ve determined that it’s become inactive. You may forget that it’s obsolete and send an email later.
- Confirm with the recipient. If you’re unsure of someone’s email address and have another way to reach them, like via phone or text, ask them directly to avoid a bounced message.
Taking these extra steps may only take a moment, but they’ll save you the hassle of undeliverable emails — and you’ll save time and energy while you’re at it.
#2. Your email is undeliverable due to spam filters
You’ve crafted the perfect email, hit send, and… silence. Are they ignoring you? That’s a possibility. It’s also possible your message ended up in the recipient’s spam folder, a digital no man’s land where even legitimate emails can disappear.
Spam filters are designed to protect inboxes from junk mail, but sometimes, they flag the wrong messages. They could be flagging you.
So, why does this happen? Spam filters analyze email content, sender reputation, and technical details. If your message contains certain red flags — like excessive links, misleading subject lines, or too many capitalized words — it might be mistaken for spam.
You can avoid the spam trap with a few adjustments:
- Craft a clear subject line. Avoid clickbait or overly dramatic phrases like “HURRY NOW!!!” or “WIN BIG!” Opt for honest, concise subject lines that match the content of your email. If it seems spammy, ESPs may think it is!
- Balance visuals and text. Emails with too many images and not enough text can raise suspicions. Aim for a good mix to ensure your message looks professional and trustworthy.
- Mind your language. Gratuitous use of words like “free,” “guaranteed,” or “urgent” can be spam triggers. Use them sparingly and within context.
- Authenticate your email. Ensure your domain is properly configured with SPF, DKIM, and DMARC settings to boost your sender reputation.
- Test before sending. Tools like an inbox placement tester can analyze your email and flag potential issues.
By paying attention to these details, you can bypass spam filters and ensure your emails reach the inbox. After all, what good is a great message if no one ever reads it?
#3. Your email can’t be delivered due to full inboxes
It’s not you, it’s them.
Sometimes, the problem isn’t your email—it’s the recipient’s inbox. When someone’s inbox is full, their email provider stops accepting new messages until that person clears mailbox space.
This can happen with accounts that have limited storage or users who don’t regularly manage their email. Maybe they go long periods without checking and deleting emails and they pile up.
When your email bounces back because of a full inbox, here’s what you can do:
- Wait and try again later. Often, recipients will clear space after noticing their inbox is full. Give it a few days before you resend your message.
- Reach out through another channel. If the email is time-sensitive, consider following up via text, phone call, LinkedIn or a messaging app to let them know you’re trying to reach them.
- Ask for an alternate email address. If the issue persists, politely ask if they have another email you can use to contact them. It may spark them to do a little inbox housekeeping.
A full inbox might feel like a dead end, but patience and alternative communication can get your message across.
#4. Your recipient has server issues
Even in the digital age, technology isn’t foolproof. Server outages or technical issues on the recipient’s email provider can prevent your message’s delivery. These disruptions can happen for a variety of reasons, like maintenance, temporary overloads, or unexpected system failures.
When server issues occur, there’s little you can do immediately—but that doesn’t mean all hope is lost. Here’s how to handle it:
- Be patient. Server problems are often temporary and resolved quickly. Wait a few hours before trying to resend your email.
- Check your email status. Sometimes, your email provider will give you a notification about the delivery attempt, which can confirm if the issue is on the recipient’s side.
- Reach out another way. If it’s urgent, consider contacting the recipient through a different method, such as a phone call or messaging app.
- Resend strategically. Once you’re confident the server issue has been resolved, send your message again. Avoid sending it repeatedly during the downtime, as this could trigger spam filters.
While server issues can be inconvenient, they’re usually temporary roadblocks. A little patience and flexibility can ensure your email eventually gets through.
#5. Your email may be on a blacklist
If your emails are consistently bouncing or landing in spam folders, your email address — or even your entire domain — might be on a blacklist. Email providers use these lists to block senders with a history of spam-like behavior, but legitimate users like you can get caught in the crossfire.
Why does this happen? Sometimes, it’s due to sending too many emails in a short period, using flagged content, or your email being marked as spam by too many people. Even if it wasn’t your fault, being blacklisted can impact your deliverability.
Here’s how to fix and prevent it:
- Use a blacklist monitor. Use tools to see if your email address or domain is on a blacklist. Prevention is far better than a cure when it comes to blacklists.
- Follow best practices. Send emails only to people who have opted in to receive them, avoid spammy language, and space out your messages. The best way to stay out of trouble, is to avoid any semblance of poor email practices.
- Authenticate your email domain. Ensure you’re using SPF, DKIM, and DMARC protocols to verify your emails as legitimate.
- Reach out for removal. If you find your domain on a blacklist, contact the blacklist provider to request removal. Many have a process for delisting if you can prove you’re not sending spam.
- Monitor your email activity. Keep an eye on bounce rates, open rates, and complaints. Unusual activity can signal potential issues before they escalate.
Being blacklisted can feel like an overwhelming problem, but with the right steps, you can rebuild your reputation and ensure your emails reach their intended audience.
#6. Your email attachments are too large
Attachments are a convenient way to share files, but if they’re too large, your email might never reach the destination. Most email providers have size limits for incoming and outgoing emails, typically ranging from 10 MB to 25 MB. If your attachment exceeds these limits, it could result in a bounce or an undelivered message.
Here’s how to handle large files effectively:
- Compress your files. Use file compression tools (like ZIP or RAR) to reduce the size of your attachment. This often makes it small enough to send via email.
- Use cloud storage. Platforms like Google Drive, Dropbox, or OneDrive let you upload large files and share a download link instead. This not only ensures deliverability but also keeps the recipient’s inbox tidy.
- Use a sender service. There are file transfer services, like WeTransfer and Hightail, that let you upload files to their website along with the recipient’s email address. These sender services send an email on your behalf with a link to download the file(s).
- Check file formats. Some file types, like images or PDFs, can be optimized for smaller sizes without losing quality. Tools for resizing or converting can help.
- Split your files. If possible, divide large files into smaller parts and send them across multiple emails. Label them clearly so the recipient knows how to reassemble them. For example: “Photos 1-4,” with the next email using the subject line “Photos 5-8 – final.”
Oversized attachments might be a common issue, but it’s also an easy one to solve. By managing your files wisely, you can ensure your important documents reach their destination without clogging up anyone’s inbox.
What to do when emails go undelivered
When an email doesn’t land where it should, review the bounce-back message for clues. Check for typos, verify the recipient’s address, and consider alternative ways to reach them if the issue persists.
Also, testing your email for spam triggers and ensuring your attachments aren’t oversized can help avoid repeat problems. Ensuring there are no email address issues ensures that you aren’t chasing a dead end.
Don’t get frustrated – there’s always a solution
Email mishaps happen, but most are easily fixed with a little patience and attention to detail. You can improve deliverability and ensure your messages get where they’re needed by addressing common issues like incorrect addresses, spam filters, or large attachments.
Where there’s a will, there’s a way.