Deliverability
How to check if an e-mail address is valid for free
Free ways to check an e-mail address: syntax, MX lookup with dig or nslookup, disposable and role flags, why SMTP probing backfires, and when to pay.
10 min read
Articles tagged “Deliverability”
22 articles.
Developers
How to check if an e-mail address exists without sending an e-mail
What syntax, MX, disposable-domain and mailbox checks can tell you without sending mail, why SMTP probing gives false answers, and tested code in Node, Python and PHP.
11 min read
Deliverability
Number recycling and phone-list decay: how often to re-check your list
Disconnected phone numbers are reassigned to new people, so every list decays. How recycling works, what the US rules say, and a re-check cadence recipe.
7 min read
Deliverability
10DLC registration explained for developers
How US 10DLC registration works: brands, campaigns, timelines, published fees, throughput, why registered messages still get blocked, and list hygiene.
7 min read
Guides
Yahoo email checker: how to check if a Yahoo Mail address exists, one at a time or in bulk
To check if a Yahoo email exists, send a test message and read the bounce, or run an account check in bulk. SMTP probes fail at Yahoo; here is why.
15 min read
Deliverability
Direct-to-carrier SMS explained: direct routes, aggregators, grey routes and how to test yours
What direct-to-carrier A2P SMS really means, how it differs from aggregator, grey and SIM farm routes, and six tests to check whether your route is direct.
13 min read
Deliverability
"This number cannot receive SMS": what the error means and how to check a number before you send
Why a number is not SMS-capable (landline, toll-free, VoIP, invalid, opted out), what the API error codes mean, and how to check a number before you send.
14 min read
Deliverability
Email-to-SMS gateways in 2026: which US carriers still support them, and what to use instead
Email to SMS gateway list for US carriers in 2026: AT&T ended email to text in June 2025, Verizon calls vtext legacy. Status, sources and what to use instead.
9 min read
Deliverability
Viber number check: a practical guide for businesses
How to check if a number has Viber, where Viber matters most, how checks relate to Viber Business Messages, and a cost model for Viber-first sending.
7 min read
Deliverability
A2P SMS explained: what application-to-person messaging is and how it works
A2P SMS is text messaging sent by software for a business. How it differs from P2P, sender types, what drives cost, deliverability and SMS pumping risk.
8 min read
Deliverability
SMS delivery reports (DLR): what each status really means
What an SMS delivery report is, what DELIVRD, UNDELIV, EXPIRED and REJECTD mean, why 'delivered' isn't proof of reading, and why DLRs go missing or wrong.
7 min read
Deliverability
What is RCS? Rich Communication Services explained for businesses
RCS (Rich Communication Services) upgrades SMS in the default messaging app. What the spec covers, RCS vs SMS and chat apps, and how to check who can get it.
7 min read
Deliverability
When does an HLR lookup pay for itself? Break-even math for SMS and OTP costs
A simple cost model for pre-send checks: when an HLR, MNP or carrier lookup costs less than the SMS it saves, with formulas and a worked table.
9 min read
Guides
Role-based e-mail addresses: accept, flag or block?
What role-based e-mail addresses are, when to accept, flag or ask for a personal address, and how to detect them without false positives.
8 min read
Guides
E-mail verification: the complete 2026 guide
E-mail verification explained step by step: syntax, MX, mailbox, catch-all, disposable and bounce checks, account signals, privacy rules, and which check fits which job.
10 min read
Deliverability
How to choose a messaging channel by country
WhatsApp, Telegram, Viber, LINE, Zalo, RCS or SMS? How to pick a channel per country for messages customers expect, and measure it on your own base.
7 min read
Deliverability
RCS capability check: what it tells senders before they send
To test if a number supports RCS, run a capability check: capable, not capable or unknown, before you send. Plus test numbers, iPhone support and SMS fallback.
9 min read
Guides
E-mail verification vs account existence checks: what's the difference?
Mailbox validation says an address can receive mail. An account check says it is registered on a service. When to use each, and the privacy rules.
8 min read
Guides
HLR lookup vs MNP lookup vs number validation: what each one answers
Validation checks the digits, MNP finds the current network, HLR asks the network if the number is live. What each answers, costs and misses.
7 min read
Deliverability
How to clean a phone number list in bulk, step by step
A step-by-step way to clean a phone list with the MobileValidate jobs API: free estimate, dedupe, invalid rows, capped cost, CSV download and data purge.
8 min read
Deliverability
SMS delivery receipts vs HLR lookup: before or after you send
A delivery receipt reports what happened after you sent an SMS. An HLR lookup asks the network before you send. What each can see, miss and cost.
7 min read
Deliverability
Why SMS messages aren't delivered: a cause tree with fixes
A cause tree for undelivered SMS: invalid numbers, unreachable phones, wrong line types, carrier filtering and handsets, with a fix for each.
7 min read
