The short answer
The unwanted delivery reports are probably backscatter. A spammer sent mail while pretending it came from your address. When some of those messages could not be delivered, automated systems returned the failure notices to the address written in the sender field: yours.
The spammer did not necessarily enter your mailbox. Email was designed in a more trusting age, and the visible sender on a message can still be forged—much like writing somebody else’s return address on a paper envelope.
You can receive the consequences of a journey you never began.
How backscatter is created
- A sender chooses an innocent email address and puts it on a batch of junk messages.
- Some messages go to addresses that do not exist, have full mailboxes or reject the mail.
- Those receiving systems generate delivery failures and send them to the forged address.
One forged campaign can create a sudden flock of notices. They may mention unfamiliar recipients, strange subjects or attachments you have never seen.
Does it mean your account was hacked?
Usually, backscatter alone does not prove that anybody signed into your account. Look for stronger evidence: messages in your Sent folder that you did not write, unfamiliar login activity, new forwarding rules, changed recovery details or security alerts from your provider.
If you find any of those signs, change the password from a trusted device, end other sessions, remove unknown forwarding rules and turn on multi-factor authentication. If the only evidence is a burst of bounces, spoofing is the more likely explanation.
Why can’t every filter stop it?
A real delivery-status notification is useful. It tells you when an address was mistyped or an important message failed. A filter therefore has to separate legitimate reports from reports triggered by forged mail, and older or poorly configured systems do not always provide enough evidence to do that cleanly.
If you own a domain, correctly configured SPF, DKIM and DMARC records can help receiving systems reject unauthorised mail. They improve the signal; they do not make every fake bounce disappear from every system on the internet.
What to do with mystery bounces
- Do not open unexpected attachments. A fake delivery notice can itself be a phishing message.
- Check your account activity. Look at sent mail, sessions, recovery settings and forwarding rules.
- Report or filter the notices. A temporary rule can quiet a large burst, but avoid deleting every genuine delivery report forever.
- Secure the account anyway. A unique password and multi-factor authentication are worthwhile even when spoofing—not intrusion—is the cause.
Backscatter often fades when the sender moves to another forged address. It is noisy and unsettling, but it is not automatically a disaster.
Where separate addresses help
An alias cannot stop every stranger from typing that alias into a forged sender field. It can, however, tell you which address is being abused. If the address belongs to one shop, newsletter or public profile, you immediately know the context and can retire the route without changing the address used by every other account.
That is the practical advantage of separation: not perfect prevention, but a smaller mystery and a cleaner exit.
Give the next signup its own return address.
Create an MXDuck alias