Cold email that finds its own prospects
New clients from businesses that have never heard of you.
An agentic SDR that sends from your own mailbox, on your own domain. It finds who fits, writes to each one, and books the meeting when somebody says yes.
Free forever, then $49/mo. No card.
- Free to start
- No card, and nothing to cancel
- Your own inbox
- No new domain, no new mailbox to buy
- Runs without you
- Hand it the keys and it works the list alone
Or point an agent at it. Claude, ChatGPT, Cursor, Hermes can run the whole loop end to end: find, write, send, and book the meeting. Scopes are yours to set, so a key that only drafts is one tick away.
campaign / tucson-dental
booked
Search
dentists in Tucson with Saturday hours
3 contactable of 41 found
Prospects
- Ridgeline DentalTucson, AZfront@ridgelinedental.com
- Sabino Family DentistryTucson, AZhello@sabinofamily.com
- Catalina Foothills DentalTucson, AZoffice@catalinafd.com
First email
Your Saturday hours
Noticed you opened Saturdays in March, which most practices near you still do not. We fill those slots for three other Tucson clinics. Worth ten minutes?
Then
- sent from you@yourdomain.com
- reply received, 09:14
- follow-up 1, follow-up 2, follow-up 3canceled
- three times offered from your calendar
- booked, Thursday 10:00invite sent
An illustration of one prospect, start to finish.
It runs on its own, unless you would rather it did not
One engine, one dial. Most people start with the gate on for a week and turn it off once they trust what it writes.
Autopilot
It runs the whole thing
One switch and it works the list alone: finds the businesses, writes each one, sends from your mailbox, follows up. Somebody asks for a call and it books one. You wake up to a calendar.
Off until you turn it on, recorded with who threw the switch and when, and off again whenever you like.
Co-pilot
Or it stops and shows you first
The same engine, with a gate before the send. Drafts wait in Review, you change what you want, and press send. Worth using for the first week on a new list, and worth turning off after.
What a new workspace does without being asked, so nobody reaches autopilot by not reading a screen.
The part nobody else will put in writing
Four things we guarantee, and what enforces each
Not “risk free”. A promise you cannot check is a nicer way of saying trust us, and this is a category where everybody says that.
- It will not send anything you would be embarrassed by
- Every draft is checked for the phrases that get cold email deleted, and a batch is checked for having quietly become one email with the name swapped. That check argues against our own drafting step. Run it with a review gate for the first week if you would rather watch it work.
- We will not get your mailbox suspended
- Your daily limit is whichever is lower: the one you set, or the one your provider enforces. So MastroSDR cannot be told to push 5,000 a day through a Gmail account that Google cuts off at 500. Crossing that limit suspends the account. The ceiling is not yours or ours to raise.
- Anyone who says stop is never contacted again
- Unsubscribes and dead addresses go on a do-not-contact list checked before every send, and those entries cannot be deleted by anyone, including you. Reply to a cadence and it stops for that person the moment MastroSDR reads your mailbox, whether you are sending through Gmail, Outlook or Resend.
- It will not book you into two places at once
- Times come from your real calendar, never from a guess, and at most one a day is offered. If the calendar cannot be read, MastroSDR says so rather than treating silence as a free week. The slot is checked once more in the seconds before the invite is written, because you may have booked something else since offering it.
- We never make a penny on the writing
- Paid plans include a fixed pool of drafts. Past it you connect your own provider key and they bill you at their rates, or you point MastroSDR at a model on your own machine and nothing leaves it. There is no per-word tier, because a vendor paid by the word has a reason to write you worse emails. Voice calls are the one thing resold above cost, at 2.5 times what the call actually cost, and you can bring your own key there too.
This is the whole product
Review
Read what is about to go out
Every first email waits here when the gate is on. Edit anything, then send with Ctrl and Enter and land on the next one. Each draft carries the deliverability score it was given and why.
Overview
And what your numbers actually mean
Not just the reply rate. Whether the problem is your list, your writing, or something that happens after the reply, read against published benchmarks rather than against nothing.
Where
Which markets answer, and which ones never do
Every place you have sent to, with its own reply rate beside it. A rate needs ten sends behind it before it appears at all, because under that one person changing their mind moves it by ten points.
It works with what you already have
No new domain, no new mailbox, no model you have to go and choose. Connect the one you use and start.
Write with
Bring a key, use the drafts in your plan, or run a model on your own machine.
Nobody hires the best. They hire the one who got in touch. Most people never get in touch.
How it works
Five steps. You can hand over as many of them as you like, in any order, and take any of them back.
Start for $0Get a list, or bring one
Search a trade and a city and MastroSDR finds real businesses with the contact address they publish themselves. Or paste your own as text or CSV. Either way, duplicates and anyone who previously opted out are filtered on the way in.
The model writes
Paid plans include the drafts, so there is nothing to connect. Or bring your own provider key, or point MastroSDR at a model running on your own machine. Each email is built from your pitch and that prospect's details, in 60 to 90 words with one clear ask.
You review
Every draft is editable, and each one is checked for the things that get cold email filtered: trigger words, link count, length.
Send and follow up
Send from the mailbox you connected, at a pace that respects your provider's own daily limit. Follow-ups go out on your schedule and stop for good the moment someone replies, which MastroSDR notices by reading that mailbox rather than waiting for you to remember.
It books the meeting
Somebody asks for a call, and the reply gets answered: their message is read, your calendar is checked, and two or three times that are genuinely free go back. They pick one and it lands in both calendars with an invite. You approve the words first, until you decide not to.
Call the ones who answer
Not every reply asks for a meeting. Those land in a callback list with the number their business publishes and how long they have waited. This is the only part of outreach measured in minutes, and the part most people lose.
Two ways to run the model
Pick one, change your mind later. Whichever you choose, MastroSDR never takes a margin on tokens.
Connect your own key
- Available on every plan, including Free. Your provider bills you directly at their rates, your prospect data goes through your account, and you can switch model whenever you like.
Point it at your own machine
- Anything that speaks the OpenAI chat format works. Give MastroSDR the base URL and the model name and your prospect data never reaches a model vendor at all.
What it costs
One price per workspace. Bring your own model key or run a model on your own machine, and we never take a margin on tokens.
Yearly works out at more than two months free
Free
$0forever
Prove it works on a real list before you decide anything.
- 100 prospects
- 500 found by search a month, unlimited pasted
- 5 mailboxes
- 300 generated drafts a month
- 50 sends a month
- 1 campaign
- Bring your own model key after that
- 1 seat
- Single-step campaigns
Pro
$49per month
A founder or a small sales team running outreach every week.
- 5,000 prospects
- 5,000 found by search a month, unlimited pasted
- Unlimited mailboxes
- 9,000 generated drafts a month
- 3,000 sends a month
- 20 campaigns
- 5 seats
- Multi-step sequences, up to 8 steps
Scale
$149per month
Several people sending, at volumes a single mailbox will not carry.
- 50,000 prospects
- 15,000 found by search a month, unlimited pasted
- Unlimited mailboxes
- 75,000 generated drafts a month
- 25,000 sends a month
- 200 campaigns
- 25 seats
- Multi-step sequences, up to 20 steps
The done-for-you tier is a person doing the setup, the list and a weekly review, and it is not something a card can provision.
Questions people actually ask
This is a category people have been burned by, so the questions are specific.
It is the thing this product is built around. Two things burn a domain: sending too much, and sending to addresses that no longer exist. MastroSDR caps both by default rather than leaving it to you to remember. Your daily limit is whichever is lower, the one you set or the one your mail provider enforces, so it cannot be talked into exceeding what Gmail allows. Every address is checked before a send is spent on it. Anyone who bounces or unsubscribes goes on a list nobody can take them off, including you. And it refuses to send at all without a postal address and a working unsubscribe link.
Probably, if you give it nothing to work with, and MastroSDR will tell you so. Every draft is checked for the phrases people say make them delete without reading, and a batch is checked for being one template with a name swapped. That check argues against our own drafting step, which is the point: a tool that only ever tells you your output is good is selling you something.
Yes, and not the way the rest of the category does. Everyone else runs a reciprocal network: your mailbox emails other customers' mailboxes, they reply, and everybody marks everything important. Google gave GMass the choice between shutting that down and losing Gmail API access in January 2023, and Apollo dropped its own warmup feature in 2024 for volume pacing. So MastroSDR ramps real sends instead. A new mailbox starts at ten a day and climbs to its full volume over three weeks, and you cannot skip it. It is slower, and it is the version that is actually true.
Because a provider reacts to a change in behaviour, not to the age of an address. Take an account that has sent five personal emails a day for six years. Two hundred cold ones on a Tuesday is a spike, however well regarded that account is. What needs easing in is the new pattern. The clock starts at your first send through MastroSDR, and reconnecting the mailbox does not restart it.
No. Connect the Gmail or Outlook you already use, including a business address on your own domain. If you would rather send from a separate domain at volume, connect Resend instead and MastroSDR will use that.
Not until you say so. Every email waits for you in Review on a new workspace, and that is the setting nobody has to find or change. Full autopilot exists and is off. Turning it on is a deliberate switch in Settings, and it records who threw it and when. You can throw it back at any time. The only other way past Review is an API key you made yourself with sending ticked, revocable in one click.
It reads the mailbox you connected, and stops that person's cadence the moment they answer. A reply goes to your inbox and never touches us, so no delivery webhook can report one. That is why most tools ask you to mark replies by hand, and why people get chased after they have already said yes.
Only a reply that clearly asks for time is answered. A question about pricing, a warm "sounds interesting", or anything the rules cannot place goes to you instead. MastroSDR reads past the quoted email underneath, so its own words asking for a call are never mistaken for theirs. It offers times your calendar says are free, at most one a day, inside the hours you set. When somebody picks one, that slot is checked again before anything is written, because the customer may have booked something else in the meantime.
It is off until you turn it on. It needs a Gmail or Outlook mailbox, because that is where the calendar is: Resend and your own SMTP server can send mail and have no calendar to read. A mailbox connected before this existed has to be reconnected to grant calendar permission, and MastroSDR says so rather than failing halfway through a reply. Every draft waits for you until you decide otherwise.
Search a trade and a place and MastroSDR finds real businesses, then takes the contact address they publish on their own website. Nothing is guessed: if a business publishes no address, it is shown without one rather than given an invented info@ that will bounce.
Describe what you sell and MastroSDR proposes groups of businesses that would plausibly care, says why for each, and checks how many actually exist before you commit. A suggestion that turns out to contain four businesses is reported as too few to tell you anything, not presented as a plan.
Paid plans include a pool of drafts, so there is nothing to connect before you start. Past that, you use your own provider key and they bill you directly at their rates. Or you point MastroSDR at a model running on your own machine, and your prospect data never reaches a vendor at all. There is no per-word tier.
No. Your prospects, drafts and replies are yours. When you use your own key or your own machine, we never see the content at all.
Yes. Prospects, drafting, sending, campaigns and the do-not-contact list are all available over a documented API and an MCP server, with scoped keys. Drafting and sending are separate permissions, so an agent can write without being able to send.
The workspace drops to the free plan at the end of the period. Nothing is deleted, and everything stays readable over the API.
In most places, for business to business, with conditions: a real postal address, a working unsubscribe, and honest headers. MastroSDR refuses to send without the first two and will not let you fake a reply thread. Rules vary by country and this is not legal advice, so check what applies where your recipients are.
Start with the free plan
A hundred prospects and fifty sends a month, no card. Enough to run a real test before you decide anything.
Start for $0Free forever, then $49/mo. No card.
Or read first, decide later
How small teams are actually winning clients from cold outreach
One teardown at a time: what they sent, to whom, what came back, and the arithmetic underneath it. No schedule, because a newsletter that goes out whether or not there is anything to say is one you unsubscribe from.
Confirmed opt-in. One click to leave, no sign-in.