How email throttling is bottlenecking the delivery of your PHI

Email throttling occurs when a server slows or limits how many messages it will send or accept at a time. Where protected health information (PHI) often moves through email, those delays create serious bottlenecks. Throttling can be triggered by sender reputation issues, recipient server limits, network congestion, or anti-spam policies enforced by ISPs.

As referenced in a 2025 BMJ Open Access commentary, a growing pattern in health infrastructure choices is that well-intended systems “leave countries and institutions vulnerable to commercial interests and extractive practices that run counter to the mission of global health.” Even routine communication systems are not immune to these pressures.

When PHI is involved, even minor delivery delays can ripple through clinical and administrative workflows. Time-sensitive messages, like lab results, urgent referrals, controlled substance authorizations, and alerts, may arrive too late to support effective decision-making. 

That kind of lag disrupts patient care coordination and slows down treatment planning. It also introduces compliance headaches. HIPAA requires covered entities to make PHI accessible to authorized users without unreasonable delay. But when emails get stuck in queues or repeatedly retried, the chances of message failure or corruption increase, threatening the integrity of electronic PHI (ePHI) during transit.

Security concerns add another layer. Even when encryption and secure transport protocols are used, throttling extends the amount of time a message remains in motion or stored temporarily on intermediate servers. The longer a message is held or resent, the greater the window for interception, timeout errors, or unauthorized access. In effect, delivery slowdowns widen the attack surface, even when the data itself is encrypted.

What throttling is and why email providers use it

Email throttling limits how many messages can be sent over a certain period, usually per hour or per day. Providers use it to keep email systems from being overloaded, protect inboxes from spam, and preserve sender reputation. According to the study ‘A General Introduction to the E-utilities’, where “all E-utility requests should be made” through designated servers optimized for performance, email platforms pace message flow to avoid congestion and rejection. 

The logic is similar to the studies warning “not to overload the E-utility servers,” since exceeding limits can trigger blocks or errors. By slowing down message output, email providers reduce the chances of being flagged as spam and improve overall deliverability.

The idea took shape in the late 1990s and early 2000s, when bulk email and spam surged alongside the rise of email marketing. Internet service providers responded by introducing throttling to curb abusive sending behavior that could strain servers or disrupt users. Over time, these controls became a core part of email infrastructure. They now function as both a safeguard and a filter, preventing server overload and minimizing system-wide delays. Throttling rules are often adjusted in real time based on factors like sender reputation, recipient policies, and overall email traffic.

The expectation of immediacy vs. reality of throttled delivery

With email, you hit send and expect the message to arrive within seconds. But that isn’t how email systems always work. Technical limits and infrastructure safeguards can quietly slow delivery, and throttling is one of the biggest culprits. Email providers, ISPs, and enterprise systems use throttling to regulate volume, prevent spam, and avoid overload. When traffic spikes or sender limits are exceeded, messages are deliberately slowed. What should take seconds can take hours, or longer, depending on the recipient server’s policies and the volume of mail moving through the system.

That gap between expectation and reality becomes especially serious in healthcare settings, where timing directly affects care. According to a study from the Journal of the American Geriatric Society, during the COVID-19 pandemic, “medical care delivery was substantially disrupted,” and delays became common across the system. In one nationally representative study, “nearly one-third (32.8%) of older adults reported delayed medical care,” and “17.6% reported that delayed care negatively affected their health.” When email is used to distribute appointment reminders, lab results, referrals, or care coordination updates, any delay introduced by throttling can compound existing barriers to access.

Throttling systems do not distinguish between urgent clinical messages and routine mass communication. Just as pandemic-era cancellations and postponements led to “reductions in emergency department visits, cancer screenings… and treatment for ongoing conditions,” delayed digital communication can similarly disrupt the timing of care. If a message containing test results or procedure updates is held in a queue, the delay can mirror the kind of care gaps older adults described, gaps that shows may lead to negative health effects when recovery of delayed care is incomplete.

Where email throttling interferes with PHI delivery

When throttling delays emails that contain PHI, the impact goes beyond inconvenience. Clinicians and staff may get information too late to act on it, which can affect treatment timing and even the quality of care. As studies like ‘Effectiveness of Email Warning on Reducing Hospital Employees’ Unauthorized Access to Protected Health Information’ have shown, “data breaches of protected health information create substantial financial, reputational, and clinical risks for patients and health care entities,” and delays can compound those risks by slowing the flow of critical updates and decision-making. 

These interruptions also make it harder to meet HIPAA requirements, since covered entities are expected to maintain PHI “without unreasonable delay” and preserve both its availability and integrity. On top of that, delayed delivery can interfere with documentation and audit trails that help in tracking, verifying, and securing PHI access.

There’s also a security angle. The longer a message sits in transit or in a queue, the wider the window for something to go wrong, whether that’s unauthorized access, message corruption, or interception. Throttling can also delay regulatory or breach-related notifications. From a risk management standpoint, it has to be paired with additional safeguards. Otherwise, PHI confidentiality, availability, and reliability can all be put at risk.

Why healthcare cannot rely on general email providers

Most generic email providers aren’t built with HIPAA in mind. They typically don’t offer the level of encryption, access control, or user authentication that the HIPAA Privacy and Security Rules require. That leaves room for unauthorized access, interception, or misdelivery of patient information. As one Cochrane Library review notes, “email is one of the most widely used methods of communication, but its use in healthcare is still uncommon,” and where it is used, “the effects of using email in this way are not well known.” That uncertainty increases the stakes when unsecured systems are used to move PHI.

These platforms also tend to fall short on requirements like audit logs and secure archiving, both needed for tracking who accessed PHI, when, and why. The review mentions “concerns regarding privacy, confidentiality, and potential misuse of information when healthcare professionals communicate via email,” including the medico-legal risks tied to non-encrypted systems. Without safeguards, standard email in healthcare can expose sensitive information and lead to legal and privacy consequences when messages are mishandled. HIPAA compliant email platforms like Paubox are built to protect sender reputation and minimize lag while maintaining compliance. 

The technical indicators of throttling

• Emails take much longer than usual to leave the outbox or reach recipients.
• Messages get queued on the server instead of sending immediately.
• You see sudden drops in delivery speed even though the system is working.
• Bounce-back notices mention rate limits, volume limits, or “try again later.”
• Only a portion of a bulk send goes through, with the rest delayed.
• Sending stops after a certain number of emails in a short time.
• Logs or dashboards show repeated retries or deferred delivery statuses.
• Messages to specific domains get slowed down more than others.
• Email traffic appears to “drip” out in small batches instead of all at once.
• ISP or server alerts reference sender reputation, volume caps, or connection limits.
  
  

FAQs

What is email deliverability?

Email deliverability is the ability of your email to successfully reach the recipient’s inbox instead of being delayed, bounced, or filtered into spam.

How is deliverability different from delivery?

Delivery means the receiving server accepted the email.

Deliverability means the email actually reached the inbox and wasn’t blocked, quarantined, or sent to spam.

What is sender reputation?

Sender reputation is a score assigned to your IP or domain based on your sending behavior. High engagement and low complaint rates improve it, while bounces and spam flags harm it.

What is throttling and how does it affect deliverability?

Throttling happens when a server limits the number of outgoing or incoming emails over time. It slows down delivery and can lead to delays, especially during bulk sending or peak traffic.