Should We Send Cold Emails Using SMTP Relay with Azure Communication Services?

Should We Send Cold Emails Using SMTP Relay with Azure Communication Services? Cold email outreach is often misunderstood as a purely technical exercise—configure SMTP, authenticate the domain, send messages, and wait for replies. On paper, it looks like an infrastructure task that any cloud platform should handle with ease. After all, if an email service exposes an SMTP relay endpoint, why shouldn’t it be used for outreach?

This assumption is where most problems begin.

In modern email ecosystems, sending an email is the smallest part of the problem. What actually determines success—or failure—is trust: trust in the sender, trust in the infrastructure, and trust built through past recipient behavior. Cold emails, by definition, start with zero trust. The recipient did not request the message, does not recognize the sender, and has no incentive to engage positively. Every interaction that follows—opens, deletes, ignores, or spam reports—feeds back into global reputation systems.

This is why cold email is not merely about delivery, but about reputation management, compliance exposure, and platform risk. A single campaign can influence how an entire domain, IP range, or cloud tenant is perceived across email networks. Unlike traditional marketing platforms that are built to absorb and isolate this risk, enterprise cloud platforms like Azure are designed around a very different assumption: that emails sent from their services are expected, transactional, and trusted.

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When Azure services enter the picture—especially SMTP Relay or Azure Communication Services—the stakes increase. Microsoft operates both the sending infrastructure and a massive portion of the receiving ecosystem (Outlook, Exchange Online). This gives Microsoft deep visibility into abuse patterns and a strong incentive to protect platform integrity. As a result, behavior that might be tolerated—or slowly corrected—on dedicated cold email platforms can trigger immediate enforcement actions in Azure.

This post does not debate whether cold emailing is effective as a sales or marketing strategy. Instead, it focuses on a narrower, more technical question: whether Azure Communication Services and SMTP Relay are appropriate tools for cold email outreach at all. Understanding the answer requires shifting perspective—from “Can Azure send emails?” to “What kind of trust does Azure expect from email workloads?”

Only with that distinction in mind does the real risk become clear.

Should We Send Cold Emails Using SMTP Relay with Azure Communication Services?

Understanding Cold Emails – What are they and what they are not

What Are Cold Emails?

Cold emails are messages sent to recipients without any prior relationship, interaction, or explicit consent. The sender reaches out “cold,” assuming neither familiarity nor expectation on the recipient’s side. This single fact fundamentally changes how email systems, providers, and users react to the message.

In practice, cold emails usually share a common set of characteristics:

Externally sourced recipients
Email addresses are often obtained from scraped websites, purchased lists, business directories, or third-party data brokers. Even when the data is technically public, the communication itself is unsolicited.
Promotional or persuasive intent
The goal is typically sales, lead generation, recruitment, partnerships, or business development—not the continuation of an existing conversation.
High likelihood of being reported as spam
Because the recipient did not ask for the email, their default reaction is defensive. Many users skip “unsubscribe” entirely and go straight to Report Spam, which is the most damaging possible signal for sender reputation.
Low engagement, high complaint risk
Open rates are generally low, replies are rare, and negative signals (deletes, ignores, spam reports) dominate. From a reputation standpoint, cold emails are statistically hostile traffic.

What Cold Emails Are Not

Cold emails should not be confused with legitimate application or service emails. They are fundamentally different from:

Password resets or account recovery emails
System alerts or service notifications
Order confirmations, invoices, or receipts
Any user-triggered communication where the recipient explicitly expects the message

These legitimate emails are sent in response to a user action or an existing relationship. Cold emails are not.

Why This Distinction Matters

Email platforms do not judge messages only by content or technical configuration. They judge intent and expectation. Transactional emails are expected and welcomed; cold emails are unexpected and often unwanted. That difference directly affects how aggressively providers monitor, filter, throttle, or block sending behavior.

Understanding this distinction is critical before choosing where and how to send emails—especially when using high-trust cloud platforms like Azure, where unsolicited behavior carries far greater consequences.

What Azure Communication Services Actually Offers

Azure Communication Services (ACS) is a cloud communication platform built specifically for application-generated, trust-based messaging. Its primary purpose is to enable software systems to communicate reliably with users who already have a defined relationship with the application or service.

ACS is designed around predictability and consent, not outreach or discovery.

Supported and Intended Scenarios

Azure Communication Services is commonly used for:

One-time passwords (OTPs) and verification emails
Identity confirmation, sign-in verification, and account security workflows.
Transactional confirmations
Order confirmations, booking receipts, billing notifications, and status updates.
Service notifications and alerts
System-generated messages such as downtime alerts, workflow completions, or policy notifications.
User-initiated communication
Messages sent as a direct result of a user action—such as form submissions, account updates, or support interactions.

In all of these cases, the recipient expects the message and recognizes the sender.

The Core Design Principle

ACS operates on a simple but strict trust model:

Known sender → expected recipient → predictable behavior

The sender identity is established and authenticated
The recipient has an existing relationship with the service
Engagement patterns are consistent and non-hostile

This predictability is what allows ACS to operate at scale with high deliverability and low abuse tolerance.

What ACS Is Not Built For

Azure Communication Services is not positioned, marketed, or engineered to support:

Cold outreach
Sales or marketing campaigns
Bulk promotional emails
Lead-generation workflows

These use cases introduce unpredictable recipient behavior, high complaint rates, and reputational risk—conditions that directly conflict with the design assumptions of ACS.

Why This Matters

Using ACS outside its intended trust model doesn’t just reduce deliverability; it triggers platform-level enforcement. The service is optimized for reliability under trust, not resilience under abuse.

Understanding what ACS is built for—and what it deliberately avoids—is essential before attempting to use it for any form of cold emailing.

Microsoft’s Email Scrutiny: Why Azure Is Different

Microsoft’s email ecosystem is unique because it controls both sides of the conversation.

Microsoft operates:

Azure, which provides the sending infrastructure (SMTP Relay, Azure Communication Services)
Outlook.com and Exchange Online, which power a massive share of the world’s receiving mailboxes

This dual role gives Microsoft end-to-end visibility into how emails behave once they leave Azure and how recipients react when they arrive. Very few cloud providers have this level of insight—and it fundamentally changes how enforcement works.

Full Visibility into Abuse Patterns

Because Microsoft can correlate sending behavior with recipient feedback, it can detect abuse quickly and accurately. Azure email traffic is continuously evaluated using signals such as:

Spam complaint rates
How often recipients click “Report Spam” instead of engaging or unsubscribing.
Bounce rates
High levels of invalid or non-existent addresses strongly indicate list-based or scraped outreach.
Engagement signals
Opens, replies, deletes without reading, and time-to-action patterns.
Content similarity and campaign fingerprints
Repeated templates, near-identical subject lines, and mass-sent content patterns that resemble marketing or outreach campaigns.
Recipient feedback loops
Direct signals from Outlook and Exchange users that feed back into Microsoft’s global reputation systems.

These signals are not evaluated in isolation. They are correlated across IPs, domains, subscriptions, and tenants.

The High-Trust Assumption in Azure

Azure email services are built on a high-trust operating model:

Messages are expected to be transactional
Recipients are expected to recognize the sender
Complaint rates are expected to be near zero
Behavior is expected to be predictable and consistent

Cold emails break every one of these assumptions by default. They introduce:

Unexpected recipients
Low engagement
High spam complaints
Unpredictable behavior patterns

From Azure’s perspective, this doesn’t look like “marketing”—it looks like abuse.

Why Cold Emails Fail Faster on Azure

On platforms built for outreach, some level of abuse is anticipated and isolated. On Azure, it is not. The moment cold-email patterns emerge, Azure’s enforcement mechanisms begin to act—often silently at first, then decisively.

Azure does not gradually adapt to cold email behavior. It actively resists it.

This is why using Azure services for cold email outreach almost always leads to throttling, blocking, or suspension—sometimes before the sender realizes anything is wrong.

The 1% Spam Complaint Threshold (Critical)

In email deliverability, there is one metric that outweighs almost everything else: spam complaints.

Across the email industry, a broadly enforced benchmark exists:

A spam complaint rate above ~1% signals sender abuse and reputation damage.

That threshold may appear small, but it is decisive. One spam complaint per hundred emails is enough to trigger defensive behavior across most email platforms—and Azure is among the strictest.

Why Cold Emails Routinely Cross the 1% Line

Cold email campaigns almost always exceed this threshold, even when they are well-written and technically compliant.

Common reasons include:

Recipients did not request the email
The message arrives unexpectedly, which immediately frames it as intrusive rather than helpful.
“Unsubscribe” is ignored; “Report Spam” is used instead
Many recipients view cold emails as illegitimate by default. Reporting spam is faster, more satisfying, and perceived as more effective.
Engagement is naturally low
Low open rates and minimal replies amplify the negative weight of every spam complaint. When few people engage positively, each complaint carries more impact.

From a reputation system’s perspective, this combination is a strong abuse signal.

What Happens Once the Threshold Is Crossed

When spam complaints exceed acceptable limits, enforcement does not happen all at once—it escalates:

Deliverability drops
Messages start landing in junk folders or disappearing entirely.
Throttling begins
Outbound email rates are reduced, sometimes silently, without explicit error messages.
Services may be disabled
Email resources or relays can be blocked, pending investigation or remediation.

At this stage, SMTP connections may still succeed, but emails no longer reliably reach recipients—a dangerous illusion of normal operation.

Why Azure Is Unforgiving Here

Azure email services operate under the assumption that:

Complaint rates should be extremely low
Recipients should recognize and expect the sender
Negative feedback should be rare and anomalous

Repeated breaches of the ~1% threshold directly contradict that assumption. As a result, Azure does not treat these events as minor issues—it treats them as systemic misuse.

Cold email behavior is not “tuned out” in Azure; it is actively suppressed.

This is why even small or “test” cold email campaigns can quickly lead to throttling, blocking, or suspension when run through Azure services.

Azure SMTP Relay: Same Risk, Bigger Blast Radius

Using Azure SMTP Relay—whether through Exchange Online or Azure-hosted applications—for cold email outreach introduces the same enforcement risks as Azure Communication Services, but with a much larger blast radius.

The key difference is scope.

When you send cold emails through Azure SMTP Relay, the behavior is no longer isolated to a single application or resource. It becomes directly associated with your Microsoft 365 tenant and its established sending reputation.

Why the Risk Is Amplified

Cold email activity sent via Azure SMTP Relay:

Ties outreach behavior to your Microsoft 365 tenant
Spam complaints, low engagement, and abuse signals are attributed to the tenant as a whole—not just the sending application.
Risks organization-wide sender reputation
Once the tenant reputation is degraded, it affects all outbound mail flows, including legitimate user-to-user communication.
Can impact every user mailbox
Deliverability issues propagate across the tenant, causing even normal emails to be treated with suspicion by external recipients.

This is fundamentally different from using a separate, disposable outreach platform.

The Collateral Damage Is Real

A single poorly planned or poorly received cold email campaign can affect:

HR emails
Job offers, interview communications, and candidate follow-ups may land in spam or be rejected outright.
Customer support communication
Ticket responses and case updates may fail to reach customers, increasing frustration and support volume.
Internal and system notifications
Alerts, approvals, and automated workflows can be delayed or dropped, impacting operations.

The team running the cold email campaign may never see these failures directly, but the rest of the organization will feel the impact almost immediately.

Why Azure Treats This as High Risk

Microsoft 365 tenants are built on shared trust. Azure SMTP Relay assumes:

Known senders
Expected recipients
Near-zero abuse signals

Cold email behavior breaks that trust model. Because the tenant is a single reputational unit, Azure responds by protecting the ecosystem—not the individual use case.

With Azure SMTP Relay, cold email misuse doesn’t just fail—it spreads.

This is why Azure SMTP Relay is often considered more dangerous than ACS for cold email outreach: the consequences extend far beyond the original campaign.

Verdict: Should We Send Cold Emails Using SMTP Relay with Azure Communication Services?

❌ Do Not Use Azure for Cold Emails

Azure email services—whether Azure Communication Services or Azure SMTP Relay—are fundamentally unsuited for cold email outreach.

They are:

Transactional by design
Built for system-to-user communication where the recipient expects the message.
Behavior-sensitive
Closely monitored for engagement patterns, complaint rates, and abuse signals.
Enforcement-heavy
Quick to throttle, restrict, or disable sending when trust assumptions are violated.

Cold email traffic conflicts with all three characteristics. Even a small campaign can trigger enforcement mechanisms that extend far beyond the original use case.

✅ Use Dedicated Cold Email Platforms Instead

If cold outreach is unavoidable, it must be handled on infrastructure that is designed to absorb risk, not punish it.

Use platforms that provide:

Reputation isolation so failures don’t affect core business systems
Separate domains and IPs dedicated solely to outreach
Explicit unsubscribe handling and throttling controls to reduce complaint rates

These platforms assume outreach behavior and are built to manage its consequences.

Final Word

Azure is a high-trust cloud platform, not a sandbox for experimentation.

Azure is not the place to test, learn, or scale cold email campaigns.

Protect your tenant, your domain reputation, and your production workloads by keeping cold email completely outside the Azure ecosystem.

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Should We Send Cold Emails Using SMTP Relay with Azure Communication Services?

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