mySMTP Deliverability Toolbox: Free Email Sender Tools

No account is required and there are no rate limits. Every check runs in your browser, so your data is never sent to mySMTP servers.

Open the Deliverability Toolbox

19 free tools for DNS, authentication, deliverability and more

Tool	Use it to
SPF Validator	Expand every `include:`, count DNS lookups (limit 10), and catch syntax errors and weak `~all` / `?all` endings
DKIM Checker	Verify a domain and selector, key type and key length (warns under 1024 bits)
DMARC Wizard	Build a DMARC record step by step: policy, alignment, report addresses and percentage
One-Click SPF / DKIM / DMARC Checker	Get a pass/warn/fail summary of all three, including alignment with your From domain

Tool	Use it to
Warmup Plan Generator	Get a day-by-day warmup schedule for a new IP or domain
Sender Readiness Checklist	Run a pre-send check of authentication, rDNS, unsubscribe and list hygiene
Blacklist Checker	Check your sending IP and domain against major blocklists, with delisting links
MailWizz Quota Optimizer	Calculate batch sizes, delivery servers and schedule for MailWizz campaigns

Tool	Use it to
BIMI Generator	Create the BIMI TXT record for `default._bimi.yourdomain.com` and preview your logo
BIMI SVG Converter	Convert a standard SVG logo to the required SVG Tiny PS format

Tool	Use it to
MX Lookup	List a domain’s mail servers, priorities and IP addresses
PTR / rDNS Checker	Confirm your sending IP has a matching reverse and forward DNS record (FCrDNS)
Bounce Code Decoder	Turn SMTP responses such as `550 5.1.1` into a plain-English cause and fix
Email Header Analyzer	Trace relay hops and delays and read SPF, DKIM and DMARC results
What Is My IP	See your public IPv4/IPv6 address, PTR and ASN
CNAME Lookup	Trace CNAME chains for tracking, bounce and DKIM domains

Tool	Use it to
Email List Analyzer	Find syntax errors, duplicates, role and disposable addresses before you import a list
Email Template Verifier	Check an HTML template for unsubscribe links, broken links and spam triggers
Password Generator	Create strong SMTP passwords locally in your browser

Situation	Start with
Setting up a new sending domain	One-Click SPF / DKIM / DMARC Checker, then the DMARC Wizard
Starting on a new dedicated IP	PTR / rDNS Checker, then the Warmup Plan Generator
Emails landing in spam	Sender Readiness Checklist and Email Header Analyzer
A message bounced	Bounce Code Decoder
Sending was suddenly blocked	Blacklist Checker
Before importing a new list	Email List Analyzer

What each record does and how to publish it

How to ramp up a new IP safely

Monitoring and delisting

Fix the most frequent sending errors