Turn signups
into replies.
The moment someone signs up for your product, ReplyBoost sends them one short email asking for a reply. Each reply teaches Gmail your domain is trustworthy — so your welcome emails, password resets and billing alerts stop landing in spam.
Free for your first 100 users · No credit card · Live in under 5 minutes
hey Maya — quick favor
hey Maya,
i'm the founder of YourApp. real talk: gmail decides if our emails reach you based on whether you reply.
could you hit reply with literally one word? "hi" works. anything.
it takes 3 seconds and genuinely changes whether future YourApp emails land in your inbox or get buried in promos.
thank you
Sent automatically from your domain the moment someone signs up. Fully editable.
Works with the tools you already use
You spent months on the product.
Half your emails never arrive.
Without ReplyBoost
- Welcome emails quietly land in Promotions or Spam
- Gmail flags your domain as low-engagement
- Activation drops 20–40% and you never see why
- You patch SPF, DKIM, DMARC — but inbox rate stays flat
With ReplyBoost
- Every signup is nudged to reply — naturally
- Gmail sees real human conversation, not one-way sends
- Activation rises because users actually read the email
- Inbox placement recovers as positive signals add up
Built for founders who ship.
A focused tool that does one thing extremely well.
Bring your provider
Resend, Postmark, or Mailgun. Drop in an API key and you're sending in seconds.
One webhook, that's it
Point Stripe, Clerk, or your own backend at our endpoint. We handle the rest.
Real deliverability lift
Replies are the gold-standard engagement signal. Watch your inbox placement climb.
Inbox simulator
Preview exactly what your users see and test the whole flow before going live.
Reply analytics
Per-project reply rates, time-to-reply, and trend lines — beautifully visualized.
Apple-clean UI
Designed for joy. Use it daily without flinching.
Three steps. Zero fuss.
"When my users sign up, they see SEND YOURSELF EMAIL PLZ on their dashboard. It sends them an email with no particular content and asks them to reply to it. It tells their email provider that emails from my business are legit. Totally recommended!"
ReplyBoost automates exactly this pattern — so you don't have to wire it up yourself.
No marketing tricks. One honest reply.
You stay in control of your sending. We do exactly one thing, and we're upfront about it.
Bring your own provider
Your keys, your domain, your sending reputation. ReplyBoost never sends from a shared IP — and never sees your password.
One nudge. Never a sequence.
Exactly one email per signup. No drip campaigns, no bulk blasts, no subscriber list to manage. It's a deliverability tool, not a marketing tool.
Cancel in one click
No contracts and no retention dance. Export your data and close your account whenever you like.
Why one reply beats every technical fix
Email deliverability is decided by reputation, and reputation is decided by engagement. Inbox providers — Gmail, Outlook, Apple Mail — watch how recipients treat your mail: do they open it, move it out of spam, and above all, do they reply? A reply is the rarest and most valuable signal a mailbox provider can see. It is almost impossible to fake at scale, so it carries enormous weight.
Authentication records like SPF, DKIM, and DMARC prove you are permitted to send from your domain. But permission is not desire. You can pass every technical check and still land in Promotions, because none of those records tell Gmail that a human actually wants your email. Engagement does — and a reply is engagement in its purest form.
ReplyBoost works because it asks for that reply at the one moment a new user is most invested: seconds after signing up. The request is small (one word is enough), honest (you explain why), and mutually beneficial. When the user replies, two things happen at once: their mailbox provider records a trust signal that protects every future email you send them, and the user themselves makes a tiny psychological commitment that increases activation and retention.
The effect compounds. Each reply nudges your domain reputation upward, which lifts inbox placement for all recipients — including the ones who never reply. That is why founders who add a reply step see fewer "I never got your email" support tickets, fewer lost password resets, and higher long-term engagement.
Frequently asked
How does asking users to reply improve email deliverability?+
Inbox providers like Gmail and Outlook treat a reply as the strongest possible signal that a recipient wants to hear from you. When a new user replies — even with a single word — the provider records genuine two-way engagement and raises your sender reputation. Higher reputation means future transactional emails (welcome messages, password resets, billing alerts) land in the inbox instead of Spam or Promotions.
What is ReplyBoost?+
ReplyBoost is a micro-SaaS tool that automatically sends one friendly 'please reply' email the moment a user signs up for your product. That single reply creates a real engagement signal that improves long-term deliverability for all of your important emails. It is a deliverability tool, not a marketing tool — exactly one email per signup, never a drip sequence.
Why do my welcome emails land in Spam or the Promotions tab?+
New sending domains have no engagement history, so providers are cautious and often route one-way bulk-looking mail to Spam or Promotions. SPF, DKIM and DMARC prove you are allowed to send, but they do not prove that people want your email. Replies do. ReplyBoost generates that missing engagement signal at signup, when users are most willing to act.
Does ReplyBoost send email from its own servers?+
No. You connect your own provider (Resend, Postmark, or Mailgun) with your own API key and verified domain. Every nudge is sent from your domain and your sending reputation — ReplyBoost never uses a shared IP and never sees your account password. Your API key is stored encrypted server-side.
How long does ReplyBoost take to set up?+
Under five minutes. Connect a sending provider, customize your one-line nudge template, and point your signup webhook (from Stripe, Clerk, Supabase, or your own backend) at the ReplyBoost endpoint. New signups are nudged automatically from then on.
How much does ReplyBoost cost?+
ReplyBoost is free for your first 100 users, with paid Starter and Pro plans for growing SaaS. You can cancel in one click and export your data at any time.
Is this the same trick indie hackers like Marc Lou recommend?+
Yes. Many indie founders manually add a 'send yourself an email and reply to it' step to warm up their domain. ReplyBoost automates that exact pattern for every signup, tracks the replies, and reports the deliverability lift — so you never have to wire it up by hand.
Your next signup deserves to reach the inbox.
Set up in five minutes. Free until your hundredth user. Cancel anytime, one click.