If you're doing cold email outreach at any meaningful scale, automated warming isn't optional -- it's the foundation of your entire deliverability strategy. The idea that you can manually warm dozens or hundreds of SMTP accounts by emailing friends and colleagues is a fantasy. In 2026, automated warming tools are the standard, and they work. But there's a critical catch: the warmup pool you choose can make or break your results. A great pool builds your sender reputation steadily. A bad pool actively destroys it. This article explains why automated warming is essential, how it works, and how to choose a provider that won't sabotage your campaigns.

What is Email Warming?

Email warming is the process of gradually establishing a positive sending reputation for a new email account or domain before sending cold campaigns at scale. During warming, your accounts exchange real emails with a network of other accounts -- called a warmup pool -- generating positive engagement signals (opens, replies, marking as important) that tell email service providers (ESPs) like Gmail and Outlook that your account is legitimate and trustworthy.

The process typically involves:

Why Automated Warming Is the Only Practical Option

There are two approaches to warming: manual and automated. Let's be direct about this -- for anyone running cold email at scale, automated warming is the clear winner and the only practical path forward.

Manual warming means sending emails to real contacts (colleagues, friends, willing participants) who agree to open, reply to, and engage with your messages. In theory, this creates the most "authentic" engagement signals. In practice, it's completely impractical:

Automated warming uses specialized tools that connect your accounts to a warmup pool -- a network of other email accounts that automatically exchange emails, generate opens and replies, rescue messages from spam folders, and create the positive engagement signals ESPs look for. This is the industry standard because:

The bottom line: if you're serious about cold email, you need automated warming. The question isn't whether to use it -- it's which provider to choose.

The Critical Factor: Your Warmup Pool Quality

This is where most people get it wrong. They sign up for whatever warmup tool is bundled with their sales automation platform or whatever shows up first in a Google search, and they assume all warmup is created equal. It absolutely is not.

The warmup pool -- the network of email addresses your accounts interact with during warming -- is the single biggest factor in whether warming helps or hurts your deliverability. Here's why:

A good warmup pool builds your reputation:

A bad warmup pool destroys your reputation:

This is not a minor distinction. Using a bad warmup pool is genuinely worse than not warming up at all. With no warmup, your accounts start from a neutral reputation and you can build it gradually through real sending. With a toxic warmup pool, you're starting your campaigns with an already-damaged reputation because the warming phase filled your account's history with bounces and negative signals.

What to Look For in a Warmup Provider

When evaluating warmup providers, these are the factors that actually matter:

Our Provider Recommendations

We've tested all the major warmup providers across hundreds of domains and accounts. Here's what we recommend:

Email Bison is our top recommendation. They run a private warmup pool that they actively maintain with genuine care -- checking DNS records, removing underperforming accounts, and keeping every address healthy. There's no premium upcharge for a better pool; their maintained pool is what you get. The deliverability results are consistently the best we've seen.

Plusvibe is a solid second choice. They take a tiered approach with multiple graded warmup pools, segmented by quality. Their system is reliable and the team actively polices their network for DNS issues and problematic senders. Just be aware that not all Plusvibe pools are equal -- ask about their higher-quality tiers for best results.

Instantly should be avoided entirely for SMTP accounts. Their warmup pool for SMTP mailboxes is extremely toxic -- over 50% of the addresses are completely invalid and undeliverable. It's the Wild West with zero maintenance. Using Instantly for SMTP warmup will actively destroy your sender reputation. You are genuinely better off not warming at all than running your accounts through their broken pool.

For a detailed comparison with more specifics, see our full warmup provider comparison article.

Best Practices for Automated Warming

Once you've chosen a reputable warmup provider, follow these practices to maximize results:

Conclusion: Automated Warming Is Non-Negotiable

In 2026, automated warming is an essential part of any cold email operation. The tools are mature, the process is well-understood, and the results are clear: properly warmed accounts dramatically outperform unwarmed ones on inbox placement.

But the warming tool you choose matters just as much as whether you warm at all. A quality warmup pool with maintained addresses, natural interaction patterns, and near-zero bounce rates will build a strong foundation for your cold email campaigns. A toxic pool with invalid addresses and no maintenance will actively destroy your sender reputation before you send a single real email.

Choose your warmup provider carefully, follow the best practices above, and give your accounts the time they need to build genuine reputation. Your future campaign results depend on getting this right.