Why “just a typo” matters
What may seem like a minor email error or simple address or domain misspelling can escalate into significant security breaches or data exposures. Some of the major factors:
- When an email is sent to the wrong recipient because of a mistyped address (e.g., missing a letter, swapped characters), sensitive data can go to unintended third-parties. (Zivver)
- Attackers exploit typosquatting or look-alike domains (e.g., a missing dot, or a similar TLD) to harvest mis-sent messages or pose as trusted senders. (Tech Monitor)
- Human error (fatigue, stress, remote work, multitasking) increases likelihood of such typos or mishandled emails. (Help Net Security)
- Because many organisations focus on inbound threats (phishing, malware) they may overlook outbound mis-sendings or simple address errors, creating a blindspot. (Zivver)
Hence: “Beware of Typos” is not trivial — these errors can feed into data leaks, regulatory violations, reputational damage and even targeted attacks.
Full details & data
Here are some key stats and findings:
- According to the UK’s Information Commissioner’s Office (ICO), in a given period misdirected emails (sent to incorrect recipient) were the top cause of reported security incidents — the figure suggests that in one quarter mis-sent emails led to 44% more incidents than phishing attacks. (Egress)
- In one survey from Tessian (“Psychology of Human Error”): 40% of employees said they had sent an email to the wrong person; 29% said their business lost a customer as a result. (Security Info Watch)
- The 2025 report by Abnormal AI finds that 98% of security leaders consider mis-directed email (i.e., human error in recipient, wrong attachments) a “significant risk”, and 96% said their org had experienced data loss/exposure from such mis-directed emails. (Silicon Canals)
- A deep-analysis of email delivery failures found that 3 million+ (≈9.2%) of certain email bounces were due to domain/username typos (receiver address incorrectly typed) and that many of these mis-typed domains are available and exploitable by attackers. (Ruixuan Li)
- In one historical example, researchers for Sophos set up doppel-domains matching Fortune 500 companies with missing dots and collected ~120,000 mis-sent emails in 6 months — including trade secrets, passwords, network diagrams. (Tech Monitor)
Case Studies
Case Study A — US Military emails mis-sent to wrong TLD domain
- Over many years, emails addressed to “@something.mil” were instead routed to “@something.ml” (Mali’s country-TLD) due to typos. (virtru.com)
- The emails included hotel bookings and travel info for senior military personnel — though there’s no public record of those mis-sent messages being exploited, the potential is significant (personnel tracking, social engineering).
- Commentary: A simple typo or incorrect TLD can change the entire destination. Sensitive operational information can leak not because of hacking, but because of address error.
- Take-away: Critical domains (e.g., government/military/finance) must implement strict sending rules, address autocomplete safeguards, and outbound checks for domain mistypes.
Case Study B — Corporate misaddressed email leading to data leak
- In one company, an employee selected a wrong email contact (due to autofill), and sent a sensitive document to an unintended recipient. As noted in one survey, “33% of employees send the wrong attachment, 32% send to the wrong recipient”. (Zivver)
- The result: Customer data leakage, regulatory obligation to notify, loss of trust.
- Commentary: This type of mistake is internal (not malicious) but the consequences mirror those of an external attack. Because the event is “just a typo” it’s easy to under-prioritise controls.
- Take-away: Outbound email controls (DLP, recipient verification, auto-prompts) are just as important as inbound spam/phishing controls.
Case Study C — Typosquatting domain harvested mis-sent emails
- Researchers set up domains like “company.com” vs “companycom.com” or “company.co.uk” vs “company.co.uuk” etc, then collected emails mis-addressed by users. The mis-sent messages included very sensitive content (passwords, invoices, diagrams) because the sender didn’t notice the typo. (Tech Monitor)
- Commentary: Attackers don’t always need to hack — simply owning the mis-typed domain gives them access to whatever is mis-sent.
- Take-away: Organisations should monitor typosquatting domains for their brand, consider purchasing likely mis-typed domains, and use mail-server rules to catch outbound to “similar looking” domains or warn users.
Why this happens (causes & contributing factors)
- Autocomplete in email clients: Users pick the wrong entry because of proximity, fatigue or being rushed. (TechTorge)
- Mistyping domain names or usernames: e.g., missing dot, extra letter, swapped characters. Studies show omission is often the error (37% in domain typos) in one analysis. (Ruixuan Li)
- Use of CC instead of BCC, incorrect attachment selected, or wrong file version. (TechTorge)
- Remote work, multitasking, fatigue, stress increasing errors. Example: 57% said they were more distracted when working from home. (UK Investor Magazine)
- Lack of outbound monitoring tools: Many orgs focus on inbound threats; outward errors are less monitored. (Zivver)
The risks & consequences
- Exposure of sensitive/personal data (customer data, financials, trade secrets) leading to regulatory fines (e.g., GDPR, HIPAA) and reputational damage. (OAIC)
- Attackers harvesting mis-sent emails can use them for follow-on fraud, social engineering or account compromise.
- Legal and compliance implications: Data sent to wrong recipient may count as a reportable breach under many data protection regimes.
- Operational disruptions: Time and cost for remediation, notification, investigation.
- Loss of trust: Clients/customers lose confidence in data handling.
Mitigation Strategies & Best Practices
Technical / tooling controls
- Implement Outbound DLP (Data Loss Prevention) on email: check attachments, keywords, recipients outside org, similarity to past mis-sends.
- Employ recipient verification prompts: e.g., when emailing outside domain or to new address, pop-up warning, “Are you sure you want to send to X?”
- Autocomplete-filter enhancements: e.g., require confirmation when using external domain or domains that are similar but not exact.
- Purchase likely typosquatting domains for your organisation (e.g., common letter omissions/swaps) and redirect them or use them to trap mis-sent mail.
- Use email address validation/autocorrect checks: domain misspellings, TLD mismatches.
- Monitor outbound email logs for unusual external recipients, high volumes, or new domains receiving mail.
- Use BCC/CC usage scanning and prompt when many recipients or external recipients included.
- Encrypt sensitive attachments and use secure file sharing rather than sending via email.
Organisational / process controls
- Training & awareness: Emphasise that even “trusted” recipients must be validated; highlight context of typos and mis-sends.
- Encourage a culture where employees report mistakes quickly (so remediation can happen). Many are reluctant. (Security Info Watch)
- Use a two-step verification process for very sensitive attachments or new external recipients (e.g., a call check).
- Periodic audits: Review mis-sent email incidents, root-cause analysis, track patterns (e.g., particular departments, times of day).
- Configure recipient domain allow-lists/deny-lists or block list of domains known to look like yours (typosquatting).
- For remote work: recognise higher error risk when staff are distracted; adjust workflows/training accordingly.
Example policy snippet
“Any email containing sensitive customer data or PII that is addressed to an external domain must trigger a ‘confirm recipient’ prompt. Matching of outgoing domain vs organisational domain must be verified. Common misspellings (e.g., .con vs .com) should cause anomaly alert.”
Incident response steps when a mis-sent email occurs
- Immediately identify the email and recipient, and evaluate what data was sent.
- Attempt retrieval/recall if possible, or initiate contact with the unintended recipient asking deletion.
- Perform root-cause: Was it autocomplete error? Typo domain? Wrong attachment?
- Adjust controls: autocomplete filters, DLP rules, training for involved staff.
- If data breach thresholds met (sensitive data, regulatory obligations), notify proper authorities/affected parties.
- Monitor for follow-on exploitation (e.g., credential compromise, spoofing using leaked data).
Additional Commentary & Insights
- While much attention goes to sophisticated phishing or malware, “simple” human mistakes often cause major losses. The “typo” vector is low-tech but high-impact.
- Interestingly, as attackers become more sophisticated (AI-generated emails, perfect grammar, fewer errors) the opposite risk emerges: Because malicious emails look too legit, the tell-tale “typo” cues people used to rely on are no longer present. (TechRadar)
- For organisations, the blindspot isn’t just inbound threat — it’s outbound error and internal process failure. Correcting typos is not just about accuracy: it’s about preventing unintended data leakage and attack surface.
- The cost of a mis-sent email often far exceeds the cost of prevention: remediation, regulatory fines, reputational damage, potential compound attacks.
- Realistic policies must assume staff will make mistakes. So systems should be built to detect and stop mistakes, not just rely on “people being careful”.
Here are three case studies focusing on how simple email-mistakes (such as typos, wrong recipients, mistyped domains) led to security breaches — along with comments on what went wrong and what to learn.
If you like, I can dig up 5 more with varying industries.
Case Study 1: Mis-sent email to wrong recipient (human error)
- According to the Office of the Australian Information Commissioner (OAIC), “the accidental emailing of personal information to the wrong recipient is the most common cause of human-error data breaches.” (OAIC)
- Example: An organisation discovered that an employee’s email account had been compromised. A forwarding rule had been set up. That compromised account held scanned copies of client ID documents. The breach included both mis-sent/compromised emails and identity-fraud risk. (ICO)
- What happened: Because the email went to the wrong person (either by typo or mis-address), sensitive personal data was exposed.
- What went wrong:
- Insufficient check on recipient addresses / outbound controls.
- Data stored in email inboxes without extra safeguards.
- A forwarding rule (possibly induced by the attacker) allowed escalation.
- Key lessons:
- Mistyping or mis-addressing an email is not trivial — it can trigger regulatory-level breach.
- Outbound DLP, recipient verification prompts, and monitoring mail-flow outside org matter.
- Data stored in inboxes (especially PII) increases risk; consider secure document storage rather than email.
Case Study 2: Misdirected email via auto-complete / wrong recipient field
- In research by Egress Software Technologies (“10 email mistakes that lead to security incidents”), one of the frequent mistakes is autocomplete causing a wrong recipient and CC instead of BCC leading to disclosure of many addresses. (Egress)
- What happened: An employee, when composing an email, selected the wrong address (often because names are similar). The message then contained confidential information or unintended recipients.
- What went wrong:
- UI design (autocomplete) made it too easy to choose wrong recipient.
- No safeguard (prompt) when external recipient or large recipient list was selected.
- People assume “I know the person so it’s okay” but small slip = big exposure.
- Key lessons:
- Add warnings when replying or composing to external addresses, or many addresses.
- Consider restricting or warning when attachments + external recipients occur.
- Train staff on being cautious even when the name looks correct — check the email domain.
Case Study 3: Typosquatting / wrong domain leads to mis-sent/misdirected sensitive email
- While a specific major breach solely attributed to a domain typo is less publicly documented in detail, the pattern is explained in multiple sources: attackers register domains that look like the target’s (typos, missing letters, similar TLDs) and collect mis-sent emails. For example, the risk is documented in articles about typos in email addresses leading to hijacked or mis-sent mails. (Egress)
- What could happen: A user types [email protected] but mistypes domain as [email protected] (or company.con) — the domain might be under attacker control or free. The email lands in attacker inbox. Sensitive attachments or credentials are exposed.
- What goes wrong:
- No validation of outbound domains by sender.
- Domain-monitoring by organisation is lacking — plausible mis-typed versions are not registered or protected.
- Outbound email system lacks checks for “similar domain to our own” or unusual destination.
- Key lessons:
- Organisations should consider owning common mis-typed variants of their domain (brand + typos) to reduce exposure.
- Outbound rules could warn when sending to domains “very similar” to the company’s domain or to newly registered domains.
- Email systems should log and alert on messages to domains that appear similar but not exact to internal domains.
Commentary & Cross-Case Insights
- Human error remains one of the top sources of email-related data breaches. For example, the OAIC found human error (including mis-sent emails) accounted for 32% of breaches in a period. (OAIC)
- Many email-security efforts focus on inbound threats (phishing, malware) but outbound mistakes (typos, wrong recipients, mis-addresses) get less attention — yet they carry real risk of data disclosure.
- Small slip (typo, wrong click, wrong domain) can cascade into large exposures, especially when sensitive data is involved (PII, financials, IDs).
- Preventive controls (checks, prompts) + monitoring (outbound logging) + education (staff awareness) all matter.
- Technical alone won’t suffice: process (review, second checks for sensitive email) and culture (recognising mistakes happen) are vital.