GlockApps vs Validity vs Mail-tester: 11 Best Email Deliverability Tools 2026

Best for Spam folder placement

GlockApps (#1, 9.2/9.4). Top-tier inbox placement testing with a broad, international seed list and actionable reports. It also handles ISP-specific delivery issues.

Best for Large-scale sender reputation

Validity (#2, 9.0/9.4). The enterprise standard for reputation data, sender certification, and large-scale list verification. It also handles Blocklist remediation.

Best for Quick pre-send spam checks

Mail-tester (#3, 8.8/9.4). The fastest, simplest tool for a single pre-send spam check and technical audit. It also handles One-off campaign testing.

What is Email Deliverability?

Email deliverability is the measure of how successful a sender is at getting their emails into the recipient's inbox, not the spam folder or getting blocked entirely. It is distinct from email delivery, which simply confirms that an email was accepted by the receiving server. Deliverability depends on sender reputation, authentication (SPF, DKIM, DMARC), content quality, and recipient engagement.

How do these tools work?

Most deliverability tools work by using a 'seed list' of email addresses they control at various ISPs like Gmail, Outlook, and international providers. You send your campaign to this list, and the tool reports back on where each email landed: inbox, spam, or another tab. They also monitor public blocklists for your domain/IP and provide dashboards to check your DMARC, DKIM, and SPF records.

How to choose

1. 1First, assess your sending volume. High-volume senders (over 1 million emails/month) should prioritize platforms with deep reputation monitoring and blocklist remediation like Validity, while smaller senders can focus on platforms with strong inbox placement tests like GlockApps.
2. 2Second, determine your primary need: diagnostics or prevention. If you have an existing problem, look for tools with strong spam trap detection and content analysis. If you are building a new program, focus on tools with ongoing monitoring and DMARC reporting.
3. 3Finally, evaluate integrations. Your chosen tool must connect smoothly with your Email Service Provider (ESP) or sending platform. Check for native integrations or a well-documented API to avoid manual work.

What is the difference between email deliverability and delivery?

Email delivery means the receiving server accepted the email, but it does not specify where it was placed. Email deliverability refers to where the email actually landed, specifically whether it reached the inbox versus the spam folder, a promotions tab, or was blocked post-acceptance.

How can I check my email deliverability for free?

You can perform basic free checks using tools like Mail-tester, which often provide one free test, or by setting up free DMARC monitoring with a service like Postmark's DMARC tool. Additionally, sending test emails to your own accounts at Gmail, Outlook, and Yahoo can provide a small, manual sample of your inbox placement.

What is a good email deliverability rate?

A good inbox placement rate is generally considered to be 95% or higher. However, this can vary by industry and list quality. Rates below 85% often indicate a significant reputation or content issue that needs immediate attention. Consistently monitoring this rate is more important than a single number.

How do DMARC, DKIM, and SPF affect deliverability?

These three authentication protocols prove to receiving mail servers that you are a legitimate sender. SPF (Sender Policy Framework) lists authorized sending IPs. DKIM (DomainKeys Identified Mail) adds a digital signature to verify content integrity. DMARC (Domain-based Message Authentication, Reporting, and Conformance) tells receivers what to do with emails that fail SPF or DKIM checks, preventing spoofing and improving your domain's reputation.