Why do some cold email campaigns get dozens of replies while others die in total silence? It’s rarely the offer or the copy itself. More often than not, it’s this invisible problem: your emails aren’t getting delivered and most senders don’t even know it’s happening.
Deliverability is the silent deal-breaker in cold outreach. You can have the best leads and the perfect pitch, but if your domain is flagged or your sending habits are off, you are invisible. That’s why most outbound teams are actively turning to Instantly to launch campaigns and make sure every message lands where it should.
While Instantly is our top pick, there are other tools worth considering. We’ve cut through the noise to highlight four additional platforms that can significantly impact your email deliverability.
1. Instantly
Instantly is much more than a sending tool. It’s a full-stack cold email platform built with deliverability at its core. Instantly gives you the best shot at getting your emails opened, read, and replied to through the following processes:
Built-In Email Warmup Tool
One of the biggest mistakes in cold outreach is sending from a brand-new domain or inbox without warming it up. That tells spam filters: “This sender is unfamiliar. They may be dangerous.” Instantly solves this issue with an automated, native warmup feature that simulates real email activity before your campaigns even begin.
Here’s how it works:
- Instantly connects your inbox to a warmup network of real, verified email addresses.
- It sends and receives automated, human-like emails to and from these accounts.
- It includes auto-replies and inbox interactions that mimic natural behavior.
Deliverability Health Score
Most cold email platforms don’t tell you whether your inbox is healthy. They simply indicate whether the emails were sent. Instantly takes this a step further with a Deliverability Health Score, giving you an objective measure of your sender reputation.
What this score tells you:
- If your inbox is warming properly
- Whether you are sending too aggressively
- If your content or sending patterns are triggering spam filters
Spam Trigger Detection
Like the deliverability health score, Instantly also includes real-time spam trigger checks for your email copy.
It detects the following:
- Overused spammy words (e.g., “FREE,” “urgent offer,” “100% guaranteed”)
- Excessive formatting (e.g., too many bolds, colors, or links)
- Subject line issues
Inbox rotation and Smart Sending
Instantly handles high-volume outreach perfectly, thanks to the inbox rotation feature. It spreads out your sending volume across domains and inboxes, reducing the risk of spam flagging.
Here’s what’s you can do:
- You can connect several accounts.
- Instantly distributes your outbound emails across all of them.
- Emails are sent at random intervals, with delays and time gaps to simulate real human behavior.
Besides these features, Instantly helps keep your domain and IP clean. For instance, through authentication checks, you can set up SPF, DKIM, and DMARC for your sending domains. These are the essential identification that email services use to verify you are not a spammer.
2. GlockApps
GlockApps is built to test where your emails are landing. You send a test email to GlockApps’ seed list, and it reports your placement across each provider. It also analyzes authentication, HTML structure, and spam filter results.
You can also run an A/B test on subject lines or templates to see how those changes affect inbox reach. GlockApps doesn’t offer live warmup or sending tools. However, as a spot-check system, it’s a strong addition.
3. NeverBounce
NeverBounce is a bulk email verification tool that reviews your lists for invalid, inactive, or potentially harmful email addresses. It checks each contact against real-time data and removes undeliverable entries containing typos.
In addition to list cleaning, NeverBounce offers an API that can be integrated directly into your lead generation or CRM systems. That means you can automatically verify leads as they come in. While NeverBounce promises low bounce rates, there have been instances of higher bounce rates following verification.
4. MailGenius
MailGenius helps you test how spam filters will treat your emails before you send them. It does this by analyzing both your email content and your domain’s technical setup. MailGenius is particularly helpful for content-based problems.
If you are unknowingly using words or formatting that trigger spam filters, MailGenius will flag them. This kind of pre-send check can be valuable if you are working with new templates or targeting a fresh segment. However, MailGenius’s verification process is pretty slow. It also lacks full email marketing functionality, and its pricing may be unclear or somewhat expensive for small businesses.
5. Bouncer
Bouncer is another email verification that cleans email lists and prevents high bounce rates. It works by analyzing your contact database and identifying invalid, misspelled, or risky email addresses.
What makes Bouncer particularly useful is its speed and accuracy in processing large volumes of data. You can upload thousands of contacts and get a verified list ready for sending in minutes. It also provides a quality score for each contact, so you can segment your list by risk level. However, Bouncer’s verification process occasionally fails to complete and the cost may not be reasonable for users who only need basic verification.
Email Deliverability in a Nutshell
While it’s best to avoid landing in spam folders, it’s equally important to have a system that keeps your cold outreach alive, consistent, and scalable. Each tool covered in this guide gives you the foundation, but Instantly? It takes email deliverability a step further with its smart sending logic, warm-up, spam detection, and many more features.
Short on time?
- Use Instantly as your core cold outreach platform. It handles 90% of deliverability the smart way.
- You can track your performance in real-time via the comprehensive analytics dashboard.
