MailTwin
For online sellers: the same five questions, fifty times a week
Where is my order. Can I get it by Friday. Do you post to Ireland. Can I swap the blue one for the green. It arrived damaged. If you sell on Etsy, eBay, Shopify, Amazon or your own site, you know the list, and you know none of it is hard. It is just relentless, and it lands in the gaps between packing, listing and the post office run.
MailTwin writes those replies. You type the points the answer has to make, and it produces the finished email in your own words. You read it and send it.
The part sellers ask about first, so here it is first
MailTwin works inside Apple Mail on a Mac. It helps with email that actually lands in your Mail app: your shop's own support address, buyers who write to you directly, suppliers, wholesale and stockist enquiries, couriers, returns, the accountant.
It does not work inside a marketplace's own messaging system. Etsy Messages, eBay's message centre and Amazon Seller Central are web systems MailTwin has no access to, and a reply typed in there is the same job it always was. Many sellers forward marketplace notifications to email, and where a buyer's message reaches your Mail app you can work on it there. But the reply usually still has to go back through the marketplace, so treat forwarding as a partial answer rather than a fix. If your shop runs almost entirely inside Etsy Messages, this is not the tool for you.
Where it earns its place is the shop's own support address and everything on the supplier side, which for most sellers is where the long emails are anyway.
What it looks like on a Tuesday
Select the message in Apple Mail, type the points your answer needs to make, and MailTwin turns them into a complete, properly written email: greeting, every point in full sentences, sign-off, in your usual register.
| You type | You get |
|---|---|
| went out Monday, tracking in the shop account, courier says Thursday, sorry it's slow | A full order-status reply with the dispatch day, where the tracking is and the expected date, apologetic without grovelling |
| yes we post to Ireland, £8.50, 5–7 days, customs charges are theirs not mine | The postage answer with price and timing, and the customs point put politely rather than defensively |
| can swap to green, same price, post the blue back unopened, refund the postage once it's here | An exchange email with all four conditions in order, so nobody has to ask a follow-up question |
| need 200 not 120 for September, same SKU, can you hold last quarter's price, when can you ship | A short trade email carrying the quantity, the date and both questions, in your supplier voice rather than your customer one |
A canned response and this are not the same thing
Every seller ends up with a folder of saved replies, and every seller ends up editing them. The template forces the same words onto a different situation. This order went out Thursday, not Monday. This buyer is annoyed and that one is not. This one asked two questions and the saved reply answers one of them.
MailTwin goes the other way round. The facts are the ones you just typed, so they are right for this order, and the message is written fresh around them. What stays constant is the voice, because it learned that from your own sent mail rather than from a template you wrote once and have half-outgrown.
Two addresses, two registers
The shop address is warm, uses the buyer's first name and apologises for the courier. The trade address is four lines and asks about lead times. Voice is learned separately for every mail account, from that account's own sent mail, so those two do not blend into one polite average. Switching mailbox switches the voice.
The one that is not a template job
Once a week something goes properly wrong and the message runs to six paragraphs: two orders, a wrong size, a threat to open a case, and a genuinely bad week behind it. That one needs a careful answer, and it is the email that eats the afternoon.
MailTwin summarises the thread so you can see what actually happened, pulls out what has been asked for, and then writes your answer at the length the person deserves. The decisions stay yours. What to refund, what to replace, what to say about the courier: you type those, it writes them out properly.
The honest version of the time saving
Christopher Naas, who makes MailTwin, says it saves him an hour or more on a busy email day. That is his experience, not a promise about your shop, and anyone quoting you a precise figure is guessing. The shape of it is the reliable part: the hours were never in the hard emails. They were in the twenty easy ones.
What it will not do
It does not connect to Shopify, Etsy or your courier, and it does not know your order data. Every fact in a reply is one you typed. It will not read your inbox on its own, answer anyone without you, or send anything you have not looked at. It will not help much if your email is mostly one-line replies. It is Mac-only and Apple Mail-only, with no iPhone or iPad app, and it needs two macOS permissions on the first run, Automation for Mail and Accessibility. That is a few minutes of clicking in System Settings and it cannot be automated away, because macOS deliberately does not let an app grant itself access to your mail.
About the AI part, in plain words
MailTwin has no AI of its own. You point it at one of eight engines and it uses that. Two of them, Apple Intelligence on macOS 26 or later and Ollama, run on the Mac itself, so the message is not transmitted anywhere. The others need a key from that provider, and the request goes from your Mac straight to them. The app keeps a running cost total, and at ordinary email volumes that is usually cents a day. There is no MailTwin server and no MailTwin account.
Common questions
Does MailTwin work inside Etsy Messages, eBay or Amazon Seller Central?
No. MailTwin works inside Apple Mail on your Mac, so it helps with email that reaches your Mail app: your shop's own support address, suppliers, wholesale enquiries, couriers, returns. A marketplace's internal message system is a website MailTwin cannot reach, and a reply to a buyer there still has to be typed there. If your shop runs almost entirely inside Etsy Messages, this is probably not the tool for you.
How is this different from a saved reply or a canned response?
A saved reply forces the same words onto a different order, which is why you end up editing it every time. MailTwin starts from the points that are true for this one, the dispatch date, the actual postage, what you have decided to do about the damage, and writes a fresh email around them in your own voice.
Can it invent a delivery date or change a tracking number?
The facts come from what you type, so if you type the wrong date you will get the wrong date, politely worded. When it rewrites a draft you have already written, a validator rejects changed numbers, dates, amounts, links and email addresses before the rewrite reaches the draft. It cannot judge whether a new sentence is true, which is why you read every message before it goes.
Can it keep my shop voice separate from my supplier email?
Yes. Voice is learned separately for each mail account, from that account's own sent mail. If the shop address and the trade address are both in Apple Mail, they keep their own registers, and switching mailbox switches the voice.
What does it cost, and does it send anything on its own?
It is a one-time licence with a 30-day full trial and no card to start. It never sends on its own. There is no autonomous mode: it writes drafts, you read them and press send.
Try it on a week of your own orders
Thirty days, every feature, no card. A busy week of real customer email settles it faster than any description does.
Other guides
- Small business owners
- Executive and virtual assistants
- Estate and letting agents
- Wedding photographers and event planners
- Charity, church and school offices
Weighing it against something else? Best AI email assistant for Mac in 2026 compares six options and says who should pick each one.