Mail Delivery Subsystem scam: what it is and how to stay safe
Mail Delivery Subsystem emails usually appear when a message can’t reach the recipient. So, seeing a subsystem email when you don’t remember sending a related message can be quite confusing. Unfortunately, scammers can present phishing as Mail Delivery Subsystem emails to trick you into clicking a link, opening an attachment, or sharing confidential info.
Of course, receiving a Mail Delivery Subsystem email doesn’t always mean you’ve been hacked. It could be a normal delivery failure. On the other hand, it could signal that someone has gained access to your account. So, you need to be vigilant.
In this guide, I dive deeper into what Mail Delivery Subsystem email is, how to spot a fake notification, what to do if you receive one, and how Bitdefender’s all-in-one plans can protect you from phishing, malware, and other online threats. Continue reading to learn all about this.
What is a Mail Delivery Subsystem email?
A Mail Delivery Subsystem email is an automated message that tells you an email you sent couldn’t be delivered. It’s usually generated by your email provider or the recipient’s mail server when something prevents the message from reaching its final destination. It’s also known as a bounce-back email because the original message returns to the sender instead of reaching the recipient.
In the subject line of this email, you are most likely to find the following messages: “Delivery Status Notification (Failure),” “Message not delivered,” or “Delivery Status Notification (Delay).”
The standard Mail Delivery Subsystem email usually includes the recipient’s address and a short explanation of what went wrong.
Why an email fails to reach its recipient
There are a few reasons why an email may fail to reach its recipient. Here are the most common ones, so you can understand whether you’re facing a scam or an issue with the email:
- Incorrect or nonexistent email address due to a typo in the recipient’s address
- Recipient’s mailbox is full and cannot accept new messages
- Recipient’s email server rejects the message due to internal security rules or technical settings
- Temporary server outages or connection problems
- Spam or security filtering may block a message if it finds the content, sender, attachment, or links suspicious
Normally, the Mail Delivery Subsystem notification will explain why the message was rejected and even tell you whether you can try sending it again later.
Is a Mail Delivery Subsystem notification a scam?
Whether or not a Mail Delivery Subsystem email is a scam depends on the sender. As I’ve discussed above, it could be a legitimate email sent by a legitimate system used by email providers to notify you when your message can’t be delivered. However, scammers can also use the familiar name as a disguise to send phishing emails.
That’s why it’s crucial for you to be able to differentiate between legitimate and fake Mail Delivery Subsystem emails.
A legitimate delivery notification refers to an email you actually sent and includes details about why its delivery failed. It also doesn’t ask you to log in, provide your password, and share personal information.
A Mail Delivery Subsystem scam relates to a message you never even sent. The sender’s address also comes from an unfamiliar domain. The email itself is likely to include suspicious links or attachments, and may require your login details. Scammers might also use language that creates urgency to pressure you into acting quickly.
How the Mail Delivery Subsystem scam works
In essence, scammers attempt to mimic the legitimate Mail Delivery Subsystem notifications to trick you into taking certain action. Here’s the most common path of the scam.
1. Scammer creates a fake delivery notification
Malicious actors may copy the design, language, and formatting that known email providers use in their Mail Delivery Subsystem emails. The message can include familiar logos, technical-looking details, and fake delivery information to make it appear legitimate. Scammers can even create a genuine-looking sender address that has a minor typo in it.
2. Message creates urgency
Scammers often rely on urgency and hasty decisions. For example, the scam email may claim that the message that can’t be delivered requires immediate attention. You may encounter such phrasing as “Your message could not be delivered,” “Action required,” “Verify your account,” or “Resolve delivery issue.” The goal is to make you act without checking first whether the message is legitimate.
3. You click a link
The Mail Delivery Subsystem scam emails often contain links to view the failed messages or take you to pages where you can, allegedly, fix delivery issues. If you’re tricked, scammers may lead you to a fake login page designed to steal your credentials. In some cases, links or attachments may even lead to malware or malicious websites.
4. Stolen information is misused
If a scammer successfully steals your login information, they can access your account as well as other services if you reused the same password. They can even use your email to send phishing messages to your contacts, access personal information, or attempt identity theft.
How to detect a Mail Delivery Subsystem scam
Because it can be hard to identify whether the Mail Delivery Subsystem message is fake, I created a checklist that will help you detect the most prominent signs. Here’s what you should focus on:
- Check your Sent folder. Start by checking whether you actually sent the email mentioned in the notification. If you can’t find it and don’t recognize the recipient, be extremely careful.
- Double-check the sender address. Don’t rely on the display name alone. Instead, check the full email address and look for unusual domains, misspellings, or addresses that don’t match your email provider.
- Don’t click suspicious/urgent links. Fake notifications often include a link asking you to view the failed message or fix the problem. I recommend hovering over the link to see where it leads. Avoid opening it if the destination looks suspicious.
- Be careful with attachments. Legitimate delivery notifications may contain technical information, but you wouldn’t need to open an attachment to solve the issue. Thus, you should never download or open attached files.
- Focus on the delivery information. Legitimate bounce-back messages usually explain why the email couldn’t be delivered. They may include the recipient’s address, a delivery status, or technical details about the error. However, if the message is vague with little to no information, but pushes you to click a link, it should be an instant warning sign.
- Watch for requests for confidential data. Always pay attention whether the email requires you to enter your password, payment details, or other personal information. As verifying your account isn’t typical for legitimate Mail Delivery Subsystem emails, make sure you don’t share your data.
Proceeding after receiving a Mail Delivery Subsystem Scam email
Even if you think that the Mail Delivery Subsystem notification is fake, you shouldn’t panic. Instead, I recommend following these steps:
- Don’t click links or open attachments. Never interact with anything in the email, unless you’ve confirmed it’s legitimate. If you need to check your account, I recommend directly opening your email app.
- Check whether you sent the original email. Carefully go through your Sent messages folder and check the recipient and subject. If you don’t recognize the message, proceed with extra caution.
- Review your account activity. Search for unfamiliar logins, devices, sent messages, forwarding rules, or connected apps. These can help you determine whether someone else has accessed your account.
- Change your password if you find signs of compromise. Set a new, strong password that you don’t use for any other account. If you reused the same password elsewhere, make sure you change it there as well.
- Enable two-factor authentication. This security feature adds an extra layer of protection by requiring an additional verification step when someone tries to sign in from an unfamiliar device or location.
- Report the email as phishing or spam. Use your email provider’s reporting option, and then delete the message. This can also help your provider identify similar emails in the future.
How the Bitdefender all-in-one plans keep you safe from fake Mail Delivery Subsystem emails
The Bitdefender Digital Life Protection plans can offer an all-in-one solution against phishing, malicious websites, malware, and online scams. For Mail Delivery Subsystem scam prevention, scam detection, email protection, and breach monitoring features can be particularly useful. Let’s explore the available plans.
Bitdefender Total Security
Bitdefender Total Security ($59.99 for the first year) provides real-time protection against malware, including ransomware, spyware, and other threats across Windows, macOS, Android, and iOS devices.
It also includes Scam Protection, which can block phishing attempts and fake websites, as well as some emerging SMS and social media scams. Thanks to this, the Bitdefender Total Security plan can help you with Mail Delivery Subsystem scams by detecting if a suspicious email is attempting to send you to a malicious website.
Along with anti-scam features, Bitdefender Total Security also offers the extra layers of protection offered by a standard VPN, password management, and cryptomining protection. There’s also parental control, but only in the Family Plan. It’s ideal if you’re looking for essential protection for your devices and everyday online activity.
Bitdefender Premium Security
Bitdefender Premium Security ($79.99/year) adds features that are particularly relevant for the protection against phishing and Mail Delivery Subsystem scams. Therefore, it’s my top recommendation if you regularly receive emails, messages, and links from unknown sources.
This all-in-one plan includes Scam Protection Pro, which provides Email Protection, Chat Protection, SMS Protection, and Web Scam Protection, plus Scamio Pro, an AI assistant that helps you identify suspicious online interactions.
The included Email Protection monitors your Gmail and Outlook mailboxes (up to 2 mail addresses) and tags incoming emails as safe or unsafe. That means a suspicious message, like a fake Mail Delivery Subsystem notification, can be flagged right in your inbox, so you know at a glance whether to avoid it before you click anything.
The Premium Security plan also includes an unlimited VPN, password manager, ad blocker, and anti-tracker, helping protect your privacy while browsing.
Bitdefender Ultimate Security
Last but not least, Bitdefender Ultimate Security ($89.99/year) is perfect if you want to monitor what happens if your personal information has been exposed, as it comes with complete security and advanced privacy features.
The package includes anti-scam and email protection features found in Premium Security, along with continuous dark web and surface monitoring, real-time breach notifications, digital footprint visualization, plus Digital Identity Protection.
These features can be useful if a phishing attempt has already exposed your email address, password, or other personal data, as they help you identify potential exposure and act quickly.
What to do if I already clicked on a Mail Delivery Subsystem scam link?
If you have misidentified an email delivery message and clicked on a suspicious link, do not panic. Mistakes happen, but you can fix them if you take action immediately. Let’s see what you can do based on a few different scenarios.
If you only clicked the link:
- Close the page
- Don’t enter any personal information
- Run a security scan on your device
- Check browser downloads
If you entered your password:
- Change the password immediately via the official email provider’s website or app
- Enable two-factor authentication
- Review account activity and connected devices or apps
If you downloaded or opened a file:
- Disconnect from the internet if you suspect malware
- Run a full security scan
- Don’t open the file again
- Consider getting professional tech help if you notice unusual device behavior.
FAQ
Is Mail Delivery Subsystem mail a scam?
No, regular Mail Delivery Subsystem emails are not related to scams. If the email is authentic, it just means that your message hasn't reached the recipient’s address. However, note that scammers have been known to use the familiar system to send malicious emails to steal confidential information.
Why am I receiving Mail Delivery Subsystem emails?
You may receive Mail Delivery Subsystem emails due to several legitimate reasons. You've entered an incorrect email address, the recipient’s mailbox is full, there’s an issue with the server and it rejects the emails, there are temporary server problems, or it may be a spam or security filtering practice of the email provider.
What should I do if I clicked a Mail Delivery Subsystem scam?
If you clicked a Mail Delivery Subsystem scam, you should immediately close the page, don't enter any information, run a security scan, and check browser downloads to inspect for malicious files.
Which Bitdefender security package protects against scams?
All three plans include scam protection. I recommend Bitdefender Premium Security for protecting your devices and sensitive data, as it also offers Scam Protection Pro, and Email Protection plus unlimited VPN. These features are enough if you receive emails, links, and messages from unknown sources more frequently. Bitdefender Total Security is best for essential protection, while Bitdefender Ultimate Security is best if you need advanced privacy protection.
