Which Mac email apps keep your mail on their servers?
Updated October 2026
Apple Mail, Mimestream, MailMate and Thunderbird connect your Mac straight to your mail provider, and their own documents say they don't keep your mail or your login on their servers. Spark, Canary and Superhuman use their servers or AI services for some features, and the new Outlook for Mac syncs Gmail and other accounts through Microsoft's cloud unless you choose otherwise. Whatever app you use, your provider (Google, for Gmail) still has your mail.
Three questions to ask about any mail app
- Is your mail kept on the company's servers? Some features need it: sending later while your Mac is asleep, sharing a draft, notifications on a phone.
- Is your login kept there? A server that checks your mail for you needs a way into your account.
- Does your mail go to AI services? Summaries and AI replies usually run on large models in the cloud, run by the app maker or by companies like OpenAI.
Using servers isn't wrong in itself. It's a trade: each of these features costs a copy of something, somewhere else.
The apps, compared
| App | Your mail on its servers | Your login on its servers | Mail sent to AI services |
|---|---|---|---|
| Apple Mail | No, it connects straight to your provider | No | Apple Intelligence runs on your Mac or on Apple's Private Cloud Compute, which Apple says doesn't store it |
| Mimestream | No | No, it stays in your Keychain | No AI of its own |
| MailMate | No | No, it stays in your Keychain | None stated |
| Thunderbird | No | No | None stated |
| Airmail | Its FAQ says messages aren't stored; Snooze Sync keeps message IDs and your address | Not stated in its FAQ | None found |
| Canary | Not by default. On iPhone and Android, push keeps the sender, subject and first line until the notification arrives | On your device; mobile push keeps them briefly | Yes, for Copilot, to providers such as OpenAI, Anthropic, Cohere and Google |
| Spark | Some: mail you send later, share or draft together; recent emails for four hours | Kept as a token Spark says it can't read | Yes, for its AI features, to providers including OpenAI, Azure OpenAI, Anthropic and Google |
| Superhuman | Its policy says it receives the emails and drafts you let it access | Not stated | Yes, to AI providers; you choose whether it trains its own models on your content |
| Outlook for Mac (new) | Yes, by default: a copy of Gmail, iCloud, Yahoo and IMAP mail syncs through Microsoft's data centers | Not stated | Not covered here |
| Edison Mail | It processes your mail to find purchases, subscriptions and travel, and shares de-identified data with business subscribers | Not stated | Not mentioned |
| Lambda Mail | No, we run no servers | No, it stays in your Keychain | No AI |
From each company's own privacy policy or help pages, read in October 2026 (linked below). Policies change, so check the current wording before you decide.
What the policies say, app by app
- Spark (policy of September 10, 2026): mail is “mainly processed on your device”, but shared emails, shared drafts and emails to send later are processed on Spark's servers. It lists how long it keeps them: recent emails for four hours, send-later emails until they're sent, shared links until you delete them.
- Canary (policy, undated): it doesn't store your mail by default. Push on iPhone and Android briefly stores your address, login, sender, subject and first line on its server. Copilot sends mail to its AI providers, which Canary says don't train on it.
- Outlook for Mac (Microsoft support pages): when you add a Gmail, iCloud, Yahoo or IMAP account, it syncs through Microsoft Cloud. To avoid it, choose “Sync directly with” your provider while adding the account.
- Edison Mail (policy of September 23, 2026): it processes your mail to find commercial messages, and shares de-identified data with business subscribers and affiliates, naming YipitData. You can opt out, but data already shared isn't removed.
- Superhuman (policy of July 6, 2026): it receives the mail and drafts you let it access, and offers a setting for whether it trains its own AI models on your content.
- Mimestream (security page, updated July 2026): it connects straight to Google, keeps your login in the Keychain, and its own services don't see your mail. Its push service passes only message IDs.
What no mail app changes
- Your provider still has your mail. A local app keeps your mail between you and Google, but Google holds it either way.
- Mail Privacy Protection in Apple Mail hides your IP address from senders and loads their images privately, so they can't tell when you open a message. It protects you from senders, not from mail apps.
- Google's rules for apps that use Gmail's API with full access: they can't use your mail for ads, sell it, train AI models on it, or let people read it without your consent. If they store or pass that mail through servers, they also need a yearly security assessment.
Where Lambda Mail stands
We make Lambda Mail, a Gmail app for Mac, so here's our answer to the same three questions.
- Your mail: it goes from Google to your Mac and is kept on your Mac. We run no servers that could store, read or pass it on.
- Your login: it stays in the Keychain on your Mac.
- AI and analytics: none. We don't know who you are unless you write to us.
That costs something too. There's no send later, and notifications arrive only while Lambda Mail is open on your Mac. It blocks known trackers and hidden images, but ordinary pictures still load unless you turn on Block all remote content, so by default it doesn't hide your IP address from senders the way Apple Mail's Mail Privacy Protection does. Our privacy page has the details.
Lambda Mail works with Gmail and Google Workspace on macOS 14 and later, and the beta is free.
More guides
Sources, read October 2026: Spark privacy policy; Canary privacy policy; Airmail FAQ; Superhuman privacy policy; Edison Mail privacy policy; Microsoft, add accounts using Microsoft Cloud and sync to Microsoft Cloud; Mimestream security and privacy; MailMate privacy policy; Thunderbird privacy notice; Apple, Apple Intelligence and privacy and Mail Privacy Protection; Google, Gmail API user data policy.