Two things can keep a newsletter out of the inbox: addresses that do not work, and settings that look like spam. Some tools here check the list. Others test an email before you send it.
NeverBounce and ZeroBounce verify addresses. GlockApps and Mail-Tester test whether a message is likely to reach the inbox. Each row shows the free plan and starting price.
At a glance
| Free plan | Starting price | |
|---|---|---|
| NeverBounce | Yes. You can get started for free with no credit card, with a free list analysis and free test credits. | Pay as you go is $8 for 1,000 credits. The Growth plan is $49 a month for up to 10,000 emails. |
| ZeroBounce | Yes. The Freemium plan is $0 a month and includes 100 validation credits that refill monthly, plus 1 inbox test. | Pay as you go starts at $39 for 2,000 validations. ZeroBounce ONE subscription is $99 a month. |
| GlockApps | Yes. There is a Free plan at $0 with 2 spam tests and 10,000 DMARC messages. | Essential: $59 a month ($708 a year billed annually). |
| Mail-Tester | Yes. Three free tests in any 24-hour period without an account. Results stay visible for 7 days, or 30 days with an account. | Monthly subscriptions start at $10 for 50 tests a month. One-time packs start at $5 for 10 tests. Prices exclude VAT. |
Prices and plans change. We checked these figures on October 10, 2026, so confirm them before you buy.
What each one is
NeverBounce
An email verification service that checks whether the addresses on a list are real and working. Cleaning a subscriber list and checking new signups to cut bounces.
ZeroBounce
ZeroBounce is an email validation and deliverability service that cleans lists and checks inbox placement for senders. Cleaning a newsletter list and protecting delivery.
GlockApps
GlockApps is an email deliverability service that tests whether newsletters land in the inbox or spam and monitors sender setup. Checking that a newsletter reaches the inbox before sending, and watching sender reputation.
Mail-Tester
Mail-Tester scores a test email out of 10 and shows what could send it to spam, so senders can fix problems before a newsletter goes out. Checking a newsletter issue for spam problems before sending.
How to choose
Start with which problem you have. If bounces are high, a list-cleaning tool checks addresses. If readers say they do not get your emails, a placement or spam test checks the message and the sender setup.
Then look at how each one charges. NeverBounce and ZeroBounce sell credits, GlockApps sells monthly plans with test credits, and Mail-Tester sells tests. Open the full page for any tool to see what it works with.
How much does NeverBounce cost?
Pay-as-you-go credits are $8 for 1,000, which is $0.008 per credit. The Growth plan is $49 a month for up to 10,000 emails. Enterprise pricing is custom.
Is there a free plan?
Yes. Freemium is $0 a month with 100 validation credits that refill monthly.
Is there a free way to test my newsletter?
Yes. You get two free tests on signup with no card, plus a free spam checker that needs no account.
How many free tests do I get?
3 free tests in any 24-hour period. Extra tests can be bought as a pack.