Understanding the Risks and Security of Shared Mailboxes

And so here I am, third coffee in and typing away, wondering about shared mailboxes. Yeah, those great but almost never well secured shared email accounts that businesses love. I’ve seen a lot in my day — I started as a network admin way back in ‘93, where voice and data multiplexing over PSTN was cutting-edge and where I witnessed Slammer worm chaos up close. Now that I run my own security gig, P J Networks and now fresh from hanging with the hardware hacking village at DefCon (still abuzz over that, fwiw), I’m confident the easiest and most frank way for them to get into any network these days is through the holes around these shared mailboxes.

Risks of Shared Mailboxes

Let’s be honest: shared mailboxes aren’t rocket science: lots of people, single inbox. Sounds efficient. But that’s also the problem.

• More users, more chance to leak a credential.
• These accounts often have super permissive access. Everyone can see everything.
• Audit trails get muddy. Who did what, exactly? Good luck figuring that out.

I worked on a bank upgrade not long ago. Three banks, I must remind you, all had shared mailboxes that were like an open door. Is it any surprise that those phishing emails slipped in through shared accounts?

And the worst part? These inboxes frequently include sensitive information — vendor correspondence, payment instructions, HR matters. Just think if a hacker was given control? Game over.

How Hackers Take Advantage of Weak Access Controls

That being said, low hanging fruit, attack vectors like weak access controls are the equivalent of leaving a car running with the keys in the ignition. Shared mailboxes are often protected by weak or reused passwords (password policies? Pfft). Once inside, hackers can:

• Use legitimate addresses to send phishing emails — much less likely to be caught.
• Some silent access to sensitive data.
• Move sideways: Pivot within the company infrastructure.

I’ve witnessed it first hand—hackers using brute force or credential stuffing attacks to crack down on shared mailbox creds, and then using that as leverage to further infiltrate. And if MFA isn’t in place? Forget about it.

Furthermore, a lot of organizations bypass role-based access control (RBAC) on top of these mailboxes. That is, all keys are shared among users. It’s like handing a dozen different cooks the same knife and assuming that no one will cut themselves.

Best Security Strategies

Here’s how to fix this mess, OK? Here’s where I get a little worked up (and possibly ranty). When it comes to securing shared mailboxes, it’s not rocket science — but you must be disciplined.

First: role-based access control (RBAC). No exceptions. Access to your shared mailbox should only be given to those who require it in their role. Period.

MFA, MFA, MFA. I know it’s a buzzword but seriously—multi-factor authentication lowers risk 99%. Password lust has its days in the past (if you still believe that complex passwords will save the day, then I have a bridge for sale).

Audit trails and monitoring. You have to be able to answer: who opened the mailbox? When? What actions would they take? But if your email system doesn’t offer this information, it’s time for a new system.

Email encryption. Please note: this is especially true for shared mailboxes with sensitive data. Step 1 Encrypt inbound and outbound emails. This means that even if a hacker snatches the mailbox, it will not give up its contents.

Regular access reviews. At P J Networks, I require clients to audit mailbox permissions on a quarterly basis. Roles change, people move on. The access list at all times should NOT be static.

Tip: On a user’s leaving, do not just disable their login: immediately change the shared mailbox password and update access logs.

Secure Email Access Solutions by PJ Networks

Since most of my readers want practical steps, here’s what we have been deploying for clients:

• Role-Based Access Control (RBAC) implementations that are suited to the business role, thus ensuring no info leakage.
• Robust email encryption solutions, from S/MIME to TLS email encryption, built in.
• Automated enforcement of MFA on all shared mailbox logins.
• Tools for real-time monitoring that notify on any early signs of strange behavior.

For banks, zero-trust architecture is far from buzzword bingo. It’s what we built directly into their email systems, where shared mailbox security is tightly integrated with identity management.

Generally speaking, I have my doubts whenever I hear of an AI-powered security tool that claims to do the impossible — I’ve seen too many a hype machine, and frankly: human decision and vigilance usually win the day.

And teaching clients a lot of security hygiene — that’s a huge part of what we do. Why Email Security Training Is Important Email security will only be as effective as the awareness of your people. The number one entry point is still phishing. So, lock those doors, but don’t forget to keep your eyes open.

Conclusion

If you leave shared mailboxes unattended, they will haunt you in some way. Businesses must stop treating them as benign utilities and start appreciating the immense risks they pose.

You don’t want your email system to be the weakest link — leaking sensitive information, facilitating phishing campaigns and, even worse, letting in ransomware.

Here’s the takeaway:

• Shared mailbox security should be taken as seriously as any other access point.
• Apply role-based access control stringently.
• Implement strong authentication, and encrypt your emails.
• Audit access, and audit permissions frequently.

I’ve been in the game for a long time — from the early days soigné with rotary modems to playing defense with banks’ digital fortresses. The fundamentals? They never change. Lock your doors, know who’s in your house and secure your keys.

If you view security as something that’s annoying or merely a checkbox that must be ticked, then brace yourself for nasty surprises. Nail these basics, and you’re lightyears ahead of the pack, a pack still gripped by outdated password lore and permissive inbox co-mingling.

Anyway, that’s it for today. Time to refill my coffee and possibly get around to answering a few of those emails. Stay safe out there.

— Sanjay Seth, P J Networks Pvt Ltd.