Updated: May 2026 | All Reviews
Quick verdict: Instantly is the complete cold email deliverability platform with warmup and sending in one. MailerCheck (MailerLite's tool) is best for list hygiene. GlockApps provides the most detailed deliverability audits. Mailgun is the best transactional email API with delivery optimization built in. And ClickUp helps you track deliverability metrics and campaign performance over time.
Rating: 5/5 — Instantly is the most comprehensive platform for cold email deliverability. It includes unlimited email warmup (gradually increasing send volume to build sender reputation), spam testing that shows exactly where your emails land in major providers, and advanced deliverability analytics including bounce rates, open rates, and inbox placement percentages. The multi-inbox management lets you scale outreach across dozens of sending accounts while maintaining reputation. Instantly also includes a built-in lead finder and email sequencer, making it the one-stop solution for cold email campaigns.
Plans start at $30/month for 1,000 active leads with unlimited warmup. Growth plan at $59/month for 10,000 active leads. For businesses running cold email at scale, Instantly pays for itself by ensuring your emails actually reach the inbox.
Rating: 4/5 — MailerCheck is MailerLite's email verification tool. It checks email lists against known invalid domains, syntax errors, catch-all addresses, and spam traps. Cleaning your list before sending improves deliverability immediately — email providers penalize senders who hit high bounce rates. Pay-as-you-go pricing at $0.01 per verification makes it affordable for any size list.
Rating: 4.5/5 — GlockApps sends your email to real test inboxes across Gmail, Outlook, Yahoo, and 50+ other providers, then reports exactly where it landed (inbox, promotions, spam) and why. The DMARC monitoring helps you configure email authentication correctly. Essential for anyone who sends high volumes and needs to prove deliverability to clients or stakeholders. Plans start at $25/month for 3 tests.
Rating: 4.5/5 — Mailgun is the leading email API for developers sending transactional emails (password resets, receipts, notifications). Its deliverability optimization includes automatic IP warmup, dedicated IPs, and real-time analytics. The flexible API, SMTP relay, and email validation service make it the technical choice for sending at scale. Free plan includes 5,000 emails/month. Flex plan starts at $35/month for 50,000 emails.
Rating: 4/5 — MXToolbox is the Swiss Army knife of email deliverability diagnostics. Check your SPF, DKIM, and DMARC records for configuration errors. Test blacklist status, SMTP connectivity, and mail server response times. Most tools are free for individual lookups. Pro plans from $14.95/month include monitoring and advanced diagnostics.
Email deliverability is not a set-it-and-forget-it activity. Use ClickUp to track your sender reputation scores, warmup progress, bounce rates, and campaign conversion metrics over time. Create recurring tasks for weekly deliverability checks and monthly list cleaning. When something changes — like a sudden bounce spike — you'll have the historical data to diagnose the issue quickly.