Emails not being sent can be a real pain. You don’t want to worry about email delivery. Email deliverability is a critical part of email communication and email marketing campaigns. If your emails aren’t delivered, you’re not reaching contacts, and your efforts are wasted.
There are several factors that can affect your email deliverability, from your sender reputation and the content of your emails to the IP address of your server. To make sure that your emails are delivered, you need to be aware of these factors and take steps to correct them.
Thankfully there are a few ways to diagnose and fix this issue. We’ll discuss the 7 most common problems and ways to fix them. Some issues are more common for email communication, others for email marketing campaigns. We’ll highlight this below each header.
1. Check your sender reputation
For email marketing campaigns
Your sender reputation is one of the most important factors that affect your email deliverability. If you have a high spam score, your emails may get blocked or sent to the spam folder.
You can check your sender reputation using tools like MxToolbox or SenderScore. These tools will give you a score based on your domain’s IP address and the number of spam complaints that have been filed against it.

If you have a low sender score, you can improve it by monitoring your bounce rate. This is the percentage of emails that are returned as undeliverable. A high bounce rate shows that your emails are not getting through to recipients, which can damage your sender score.
Another way to improve your sender score is by keeping your email list clean. Remove any invalid or inactive email addresses from your list. And don’t send too many emails to recipients who do not engage with your messages.
2. Verify your email addresses
For email marketing campaigns
If you’re having trouble sending emails to certain recipients, it could be because their email addresses are invalid. You can verify email addresses with email verification tools, like Bouncer or MailerCheck. These tools check if the email addresses on your list are active or not. Read our full Bouncer review to learn how it works.
Verifying emails helps you maintain a high sender score and email reputation. And you won’t waste time and money on junk leads.
Some email addresses will become inactive over time. When people leave their companies, their corporate mail addresses become inactive. To avoid negative consequences, regularly validate your list with email verification software.
3. SMTP Authentication
For email communication and email marketing
A common reason why emails may fail to send is an SMTP authentication error. This occurs when the SMTP server requires a valid username and password to send emails. This is the most common authentication method. But it might be different for your email client. If your SMTP settings are incorrect, you’ll receive an error message.
To fix this, you’ll need to update your settings, so they match the SMTP server. Once you’ve done this, you should be able to send emails without any problem. If you’re not satisfied with your SMTP provider, check out our guide with the best free SMTP servers.
4. Network Connection Errors
For email communication
There could be a general network issue that is causing problems with sending email. If this is the case, you may want to try again in a few minutes. If the issue persists, it could be a DNS or internet connection issue. Make sure you’re connected to the internet.
DNS stands for Domain Name System, and it handles translating domain names into IP addresses. If there is a problem with DNS, you won’t be able to send emails.
You can check to see if there is a DNS issue by trying to send your email to an alternate email address. If the alternate email address also does not receive your message, then you likely have a DNS issue.
To fix a DNS issue, you will need to change your DNS settings. You can do this by contacting your email provider or by using a public DNS service such as Google Public DNS. Once you have changed your DNS settings, you should be able to send and receive emails from your mail server as normal.
5. ISP Blocking Port 25
For email communication
Many internet service providers are blocking access to port 25 by default as a security measure. This means that you may not be able to send emails using your usual server settings. To work around this, you can try using an alternate port, such as 587, which is typically unblocked.

Source: Ryan Doyle
If you’re still unable to send, contact your email service provider directly to ask them to unblock port 25 for you. In some cases, they may be able to do this temporarily while you troubleshoot the issue.
It’s also possible that the problem lies with your email client or server itself. If you’re using a web-based client like Gmail, check to make sure that you haven’t exceeded your daily sending limit. If you’re using a desktop client like Outlook, try changing the outgoing server settings to match those of your ISP.
6. Check your email account passwords
For email communication and email marketing
You may have the wrong password for your email account. To fix this, simply check the login details for your email account and make sure that they are correct. If you can’t remember your password, you can always reset it using your security settings.
7. Check your content for spammy keywords
For email marketing campaigns
If you include spammy keywords in your content, your emails may be flagged as spam. This isn’t an issue if your sender reputation is good, your list is healthy, and your settings are okay.
You can check for spammy keywords using a tool like SpamAssassin or Mail Tester. These tools will analyze your content and flag any potential spam words or phrases. If you find any spammy keywords in your content, you can remove them or replace them with more benign terms.
By ruling out each of these potential causes, you should be able to identify and fix the problem so you can get back to sending emails as usual.
Email not sending: Wrap up
Email is a powerful tool but only when it’s working properly. Thankfully, by diagnosing and fixing the issue using the ways we discussed in the article, you can get your email back on track. If you’re still unable to send emails from your email marketing tool, the best way to solve it is to contact support.