When an e-mail is sent to one or more recipients, you usually assume the e-mail will be successfully received by each of them. But when an e-mail is not delivered successfully, you start to question what happened and why. Sometimes you will receive a return e-mail stating there was a problem and what it is, but not always. It can be frustrating to figure out the issue and how to resolve it.

When an e-mail is not delivered to a recipient, several reasons could be the cause. Review each link below for further information.

E-mail sent to invalid e-mail address

Sending an e-mail to an e-mail address that is misspelled or does not exist results in that e-mail not being delivered. While it seems obvious, it is easily overlooked and happens often.

  • E-mail sent to invalid e-mail address.
  • E-mail sent to Junk folder.
  • E-mail marked as spam by e-mail provider.
  • Recipient’s mail server blocked the e-mail.
  • Sending mail server listed on a blacklist.
  • Recipient doesn’t have the time to respond.

Even if it’s spelled correctly, if the e-mail address does not exist, the e-mail cannot be delivered and you will usually receive a non-delivery notification. The notification will tell you the e-mail address does not exist, isn’t found, or other important information.

To resolve these issues, verify the e-mail address is spelled correctly and that it is valid. You may want to contact the recipient by phone to confirm the spelling and validity of the e-mail address.

A non-delivery notification may be sent to your spam folder.

E-mail sent to Junk folder

E-mails can sometimes be sent to a Junk folder in the recipient’s account without them realizing it. The cause could be the recipient previously flagged your e-mails as junk by accident, resulting in all future e-mails being diverted to the Junk folder.

The e-mail client or e-mail service may also flag the e-mail as graymail, a type of e-mail not considered as spam, but also not considered as important e-mail either. E-mails flagged as graymail often are sent to the Junk folder.

To resolve an issue with e-mail getting sent to a Junk folder, ask the recipient to check their Junk folder. If the e-mail is found there, they can flag it “not Junk,” which allows messages once again to go to the recipient’s Inbox.

E-mail marked as spam by e-mail provider

Many e-mail providers have anti-spam protection built into their e-mail service. The anti-spam protection attempts to detect if an e-mail is spam, and if so, block it from being delivered. Sometimes the anti-spam protection feature gets it wrong, however, and incorrectly marks messages as spam.

If the e-mail is getting sent to a business, they may have an e-mail security system that works to detect spam e-mail. Like the anti-spam protection of an e-mail provider, a security system will try to determine if an e-mail is spam, and then block it accordingly.

To resolve an incorrect spam detection, ask the recipient to request that their e-mail provider or security system whitelist your e-mail address.

Recipient’s mail server blocked the e-mail

E-mails are sent and received through a mail server. Sometimes, a message sent from another mail server may be blocked due to suspicious content found in those which were sent previously. Suspicious content can include viruses, malware, and links to certain websites.

If you think recipients are not receiving your e-mails because the mail server is blocking them, contact the recipient by phone or through another e-mail account. Work with the recipient to determine if your mail server is in fact being blocked by the recipient’s mail server. If so, the administrator of the recipient’s mail server might consent to review the block, or make an exception.

Sending mail server listed on a blacklist

The most severe reason e-mails are not delivered to a recipient is because a mail server could be blacklisted. When a mail server sends a lot of spam or is found to send suspicious content to multiple mail servers, a company often adds the offending mail server to a blacklist. The blacklist is a way to let e-mail providers and security systems know that they should block all e-mails from a specific mail server. There are over one hundred e-mail blacklists and a mail server can be on one or more of them.

To resolve this issue, contact your e-mail provider to ask them to work with the company on which your mail server is listed.

If you work at a company and your e-mails are being blocked due to blacklisting, contact your e-mail administrator, cybersecurity administrator, or IT help desk. Let them know the company’s mail server is blacklisted and ask them to have it removed.

  • Check if a mail server is listed on an e-mail blacklist at the MxToolbox website.

Recipient doesn’t have the time to respond

If you don’t know the recipient or have no other way of contacting them to verify they’re receiving the e-mail, they may not have the time to respond. Many people, and some companies, don’t respond to every e-mail they receive and instead delete e-mails that do not interest them.

If you’re trying to reach someone not responding by e-mail, try other forms of communication, such as a website contact form or through social networking.

  • Why can’t I receive or send an e-mail?
  • Why can’t I receive any e-mail attachments?
  • How to stop spam.
  • How to block or unblock an e-mail address.
  • E-mail help and support.