One API, many providers
Adapters fetch and send through Gmail (OAuth and the Gmail API), Microsoft 365 (Microsoft Graph), and any IMAP and SMTP account. Every client uses the same API; none of them talks to a provider.
An email proxy that keeps your mail in your own database
Email, without the baggage.
Courier sits between you and your mail providers. One server fetches mail from Gmail, Microsoft 365, or any IMAP account and serves one clean API for the web client, agent tools, and apps.
Features
Your mail, in your database
Courier is a full-stack email platform: a proxy server that does the provider work, and clients that never have to. These are the jobs it does today. The web client reads, triages, searches, writes, sends, and manages rules, and the pages below say where each thing lives.
Providers on one side, one API on the other
Your own database
Every message, thread, label, and rule lives in PostgreSQL, with full-text search from a trigger-maintained index. The most recent 1,000 messages per account are kept warm in Valkey, and attachments go to S3 when a bucket is configured.
Threads that hold together
A message joins a conversation by its References header, then In-Reply-To, then the provider's thread ID, and last by subject within 30 days.
Live updates
The web client listens to an authenticated stream of server-sent events, so new mail and sync changes show up without a refresh. The header says Live when the stream is connected.
A web client for the inbox
Every folder, or all accounts at once
Inbox, Starred, Snoozed, Sent, Drafts, Scheduled, Spam, Trash, Archive, and All Mail, for one account or a unified view across all of them.
Conversations
A thread folds earlier messages to one line and opens the newest. Quoted text collapses, attachments show as chips, and a warning appears when a sender's address looks like a lookalike or fails its authentication results.
Labels and smart folders
Labels carry a color and can nest. Smart folders are saved searches that fill themselves. They list in the sidebar and open to their own page, and new ones are created through the API or an agent.
Batch actions and density
Select many messages and archive, trash, star, mark, label, or move them in one step, and switch the list between comfortable, default, and compact density.
Block and allow lists
A blocked sender never reaches the inbox, because the list is checked when mail is synced. The Settings page manages both lists.
Go-to keys
Press G and then I, S, D, T, A, P, or R to jump to the inbox, starred, drafts, trash, archive, spam, or rules. The question mark opens the shortcut sheet.
Write in Markdown. Let rules do the sorting.
A Markdown composer
A CodeMirror editor with a formatting toolbar, a rendered preview, and your signature appended. Courier turns the Markdown into clean HTML when the message is sent.
A rules engine
Sixteen condition fields, thirteen operators, and twenty actions, joined in nested AND and OR groups, with priorities and a stop-processing switch. A rule can also be run over mail that is already in the database.
Send later, snooze, undo
The server queues scheduled sends, wakes snoozed messages, and holds a send for an undo window. Send shows an Undo toast for that window, and the web client lists what is scheduled and snoozed. Times are set through the API and the agent tools.
Everything is also a tool
148 MCP tools
Reading, sending, drafting, labels, folders, rules, smart folders, contacts, signatures, accounts, search, and push are all tools an agent can call. Each is a thin adapter over a REST route, and tests fail when the two drift apart.
AI features, when a model key is set
Semantic search, thread, contact, and topic summaries, commitment and follow-up tracking, reply drafts, meeting briefings, related threads, and suggested rules run on the server and answer through the API. Without a model key each one says it is not configured instead of failing.
Approved outreach for other tools
Other Renkara tools can send outreach through Courier with proof of the exact content, an approval step, retries, a suppression list, and signed complaint and unsubscribe intake.
Screens
See it in light and dark
Real captures of the running tool, with fictional StrataForge Robotics data. They follow your theme.
How it works
From provider to inbox
Connect
Link a Gmail or Microsoft 365 account through OAuth, or an IMAP and SMTP account with an app password. Credentials are encrypted at rest.
Sync
Adapters fetch mail by each provider's own mechanism: Gmail history and push, Microsoft Graph delta and webhooks, IMAP IDLE. Courier normalizes it, threads it, indexes it, and stores it.
Read and organize
The web client, an agent, or a native app reads from Courier's API. Stars, archive, trash, and spam change Courier's copy at once and are written back to the provider.
Automate
Rules sort new mail as it arrives. Workers send scheduled messages, wake snoozed ones, and purge old trash, all on the server.
Accessibility
Built so everyone can use Courier.
Courier's web client is built on the Renkara design system. On 10/29/2026 we ran axe-core over fourteen states of the running app (the inbox, an open conversation, starred, sent, drafts, scheduled, rules, the rule editor, settings, search results, a smart folder, a reply window, contacts, and the composer) at phone and desktop widths in light and dark, 56 scans in all. It found real problems earlier in the day; we fixed the small ones in Courier, and what is left is listed below as known gaps. We do not claim a WCAG conformance level for the product.
Partly supported
Keyboard operation
A skip link and a visible focus ring are in place, every message row is a focusable control that opens on Enter or Space, and go-to chords (G then I, S, D, T, A, P, or R) and a shortcut sheet work. Courier defines more single-key shortcuts than the web client connects, so those do nothing. The scan reports no nested controls in the message rows.
Partly supported
Screen reader landmarks and labels
The page has landmarks (header, sidebar navigation, main), the Live indicator announces its state, the star buttons and message headers have accessible names, and axe-core's name and role checks pass apart from one button on the contacts page and one unfocusable scrolling pane in the reply window. Courier has not been tested with a screen reader.
Partly supported
Contrast in light and dark
After fixes, text and controls pass axe-core's contrast rule in light and dark on every scanned state except one, the name of the open smart folder in the sidebar. The scan found white text on the dark theme's light-teal accent, gray text on a hard-coded fallback color, and red text on the dark surface, and each was fixed in Courier. Only the scanned states were checked, and no one has reviewed contrast by hand.
Partly supported
Reduced motion
The header checks the reduced-motion setting before animating, and the design system's global styles switch motion off when it is set. The rest of the app's transitions have not been audited and no test covers it.
Not yet tested
Text resize and zoom
Resizing text to 200 percent has not been tested, and several components set text in fixed pixel sizes.
Partly supported
Mobile and touch
Below 768 pixels wide the sidebar folds into a menu drawer, the list fills the screen, and opening a conversation replaces it with the reading pane. No scanned state scrolls sideways at 375 pixels. Tap-target size was not measured.
Tech specs
Under the hood
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MCP tools
Built for agents as well as people
Every tool is a thin adapter over a REST route. These are the groups, with the number of tools in each and a few names.
Messages and threads · 24
list_messagesget_messageget_threadget_unread_countarchive_messagesdelete_messages
AI and search intelligence · 20
semantic_searchsummarize_threadsummarize_contactsummarize_topiclist_commitmentsget_follow_ups
Outreach controls · 20
create_outreach_draftget_outreach_draft_proofapprove_outreach_draftdispatch_outreach_draftcreate_outreach_suppressionlist_outreach_outcomes
Contacts · 13
list_contactsget_contactupdate_contactmerge_contactsexport_contactsautocomplete_contacts
Compose and send · 12
send_messagereply_messageforward_messagecreate_draftupdate_draftsend_draft
Labels and folders · 12
apply_labelremove_labelmove_to_folderlist_labelscreate_labelget_account_folders
Signatures and identities · 11
list_identitiescreate_identityupdate_identitylist_signaturescreate_signatureget_default_signature
Search and smart folders · 8
search_messageslist_smart_folderscreate_smart_folderget_smart_folderupdate_smart_folderexecute_smart_folder
Accounts · 7
list_accountsget_accountcreate_accountupdate_accountdelete_accountsync_account
Rules · 7
list_rulescreate_ruleupdate_ruledelete_ruleget_ruletest_rule
Block and allow · 6
block_senderunblock_senderlist_blocked_senderslist_allowed_sendersadd_allowed_senderdelete_allowed_sender
Service, settings, and push · 8
check_service_healthget_diagnosticsget_settingsupdate_settingsregister_push_subscriptionget_vapid_public_key
Native clients
On iPhone, iPad, and Mac
- Courier for iPhone and iPadiOS 18 and later
In development. It signs in through the system browser and reads mail: a compact list on iPhone, a three-column workspace on iPad, message detail, star, read, archive, and trash, and a chronological conversation with mute.
- Courier for MacmacOS 26 and later
In development, with the same scope as the iPhone and iPad app: sign-in, mail list, message detail, triage, and conversations.
- CourierKitSwift package
The shared library under both apps: the API client, typed account and message models, sign-in with PKCE and the Keychain, and thread loading.
FAQ
Questions people ask
Does Courier replace my mail provider?
No. Your provider still holds the mailbox and delivers mail. Courier syncs a copy into its own database and sends through your provider's servers, so your mail, labels, and rules stay yours if you switch providers.
Which providers can I connect?
Gmail and Microsoft 365 through OAuth, and any IMAP and SMTP account with an app password.
Can I send mail from the web client?
Yes. The web composer sends new messages, replies, replies to all, and forwards, and a short undo window lets you take a send back. Agents can do the same through the API and the tools.
What do the AI features need?
A model key. Without one, each AI feature reports that it is not configured instead of failing. There is a monthly budget per account, with a hard stop, and the features answer through the API and agent tools.
Where do the screenshots come from?
They are captures of the web client running locally against fictional data for StrataForge Robotics, a made-up company. No real mailbox was read, and the capture never connects to a mail server.
Contact
Questions about this tool?
Write to Renkara Media Group and a person will answer.