Self-hosted email engine.
Enterprise email client on self-hosted email infrastructure. Free @calistopro.com mailbox or custom domain with domain authentication provisioning. 3-pane inbox with keyboard shortcuts. Server-side rules engine. Team shared mailboxes. HTML signature editor. Outbound delivery with retry queue. Inbound sync.
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infrastructure layers (email engine, authentication, outbox, CDN)
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system folders + unlimited custom
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condition fields in the rules engine
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rule actions (move, label, archive, delete, forward)
Self-hosted email engine. Outbound delivery, inbound sync.
Calisto Mail runs on a self-hosted email engine on EU infrastructure. Outbound delivery handles sends with per-user auth and a retry queue. Inbound sync polls at 60-second intervals. Domain authentication auto-configured per domain.
Self-Hosted Email Engine
Self-hosted on European infrastructure. Outbound delivery with per-user authentication. Inbound sync polling every 60 seconds. No third-party email relay for transactional mail.
- Outbound delivery with per-user credentials
- Inbound sync polling
- 60-second polling interval
- EU-hosted infrastructure
Deliverability Stack
Domain authentication key generation per domain. MX and authentication records auto-configured during domain provisioning. The email engine handles spam classification on inbound. Signed outbound ensures inbox placement.
- Domain authentication key generation per domain
- Authentication records auto-configuration
- Inbound spam classification
- Domain registration on the email engine
Outbox Retry Queue
Database-backed retry queue for failed sends. Exponential backoff at 30s, 60s, and 120s intervals. Three attempts per message before permanent failure. Failed messages remain inspectable in the outbox.
- Exponential backoff (30s → 60s → 120s)
- Up to 3 retry attempts
- Database-backed queue
- Failed message inspection
Storage & Attachments
Attachments up to 25 MB routed through Box SDK to cloud storage. Served from CDN with signed download URLs. Per-mailbox storage quota metering with overage alerts at 90% and hard cap at 100%.
- 25 MB max attachment size
- Box SDK → cloud storage
- CDN delivery with signed URLs
- Quota metering with 90% overage alert
Outbound delivery. Inbound sync. One engine handles both.
Outbound messages route through the email engine with per-user authentication and a database-backed retry queue. Inbound messages arrive via sync polling at 60-second intervals, parsed and stored in Dataverse with attachments routed to Box CDN.
Draft, send, and find. The three daily verbs.
Compose with To/CC/BCC, attachments, and signature insertion. Threaded conversation view with dual thread-ID resolution. Full-text search with date, folder, and attachment filters.
Compose
Full compose form with To/CC/BCC recipient fields, subject line, and HTML textarea. Attachments up to 25 MB with inline preview. Reply and forward modes with quoted-message context. Signature auto-insertion from mailbox settings. Draft auto-save to Dataverse.
- To / CC / BCC recipient fields
- HTML textarea with signature insertion
- File attachments (25 MB max, inline preview)
- Reply and forward modes
- Draft auto-save
Six system folders. Unlimited custom. Color-coded labels.
Inbox, Sent, Drafts, Archive, Spam, Trash, built in. Custom folders with unread counts. Labels with color picker for cross-folder tagging. Snooze to resurface messages at a chosen time.
Inbox
Primary landing folder for all inbound messages.
Sent
Auto-populated on outbound send via the email engine.
Drafts
Draft auto-save from compose. CRUD via /api/mail/drafts.
Archive
Keyboard shortcut e or bulk action. Out of inbox, still searchable.
Spam
Inbound spam classification by the email engine. Automatic folder routing.
Trash
Keyboard shortcut #. Permanent deletion after retention period.
Custom Folders
Unlimited custom folders beyond the six system defaults. Each folder tracks its own unread count. Folder CRUD via /api/mail/folders.
Color-Coded Labels
Create labels with a color picker. Apply multiple labels per message. Search and filter by label. Label CRUD via /api/mail/labels.
Snooze
Snooze a message until a chosen date and time. Sets calisto_snoozeuntil on the message record. Cancel snooze to return the message immediately.
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max attachment size (Box CDN)
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storage per paid mailbox
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inbound sync interval
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auto-reply deduplication window
Server-side rules. Shared mailboxes. Per-mailbox signatures.
Rules evaluate at inbound, before messages reach the inbox. Team mailboxes share a single address across multiple members. Each mailbox maintains its own HTML signature with formatting toolbar.
Three condition fields. Five actions. Evaluated at inbound.
Rules execute server-side before messages reach the inbox. Condition builder matches against From, Subject, and To fields. Actions route, label, archive, delete, or forward. Priority ordering determines execution sequence. Toggle rules on and off without deleting them.
Conditions
Schedule-based auto-reply with configurable message. 24-hour per-sender deduplication prevents reply loops.
Actions
Shared inboxes. Per-mailbox settings. Member management.
Create shared team mailboxes with their own addresses. Add members who access the shared inbox alongside their personal mail. Each team mailbox has independent settings: display name, signature, auto-reply, forwarding, and storage quota.
Create Team Mailbox
Provision a shared mailbox with its own address. Multi-step creation form with mailbox name, domain selection, and initial member assignment.
Member Management
Add and remove team members per shared mailbox. Each member accesses the shared inbox from their own Calisto Mail interface alongside their personal mailbox.
Per-Mailbox Settings
Configure display name, signature, auto-reply, and forwarding address independently for each team mailbox. Storage quota tracked per mailbox.
Search & Filter
Search across all team mailboxes by name or address. Filter by storage quota, platform, and tier. Mailboxes API returns quota and platform metadata.
HTML editor. Per-mailbox. Auto-inserted on compose.
HTML signature editor with formatting toolbar: bold, italic, links, and image embeds. Each personal and team mailbox maintains its own signature and display name. Signatures auto-insert when composing new messages.
Formatting Toolbar
- Bold, italic, underline formatting
- Hyperlink insertion
- Image embedding
- HTML source editing
Mailbox Settings
- Display name per mailbox
- Auto-insertion on compose
- Separate signature per team mailbox
- Settings page with live preview
Four steps. Free or custom domain. Domain authentication from step one.
The setup wizard provisions a mailbox in four steps. Choose free (@calistopro.com) or bring a custom domain from Sites. Domain authentication key generation and records auto-configured. Mailbox active immediately.
Four steps. Free or custom domain. Domain authentication from step one.
The setup wizard provisions a mailbox in four steps. Choose free (@calistopro.com) or custom domain. Domain authentication key generation and records auto-configured during provisioning. Mailbox active immediately.
Choose Domain Type
Free @calistopro.com mailbox or custom domain from your verified Sites domains.
Configure Address
Free path: pick a local-part (you@calistopro.com). Custom path: select a domain from Sites, then choose local-part.
Provision Mailbox
Creates the mailbox cluster-side. Domain registered on the email engine with authentication key generation. MX and authentication records auto-configured.
Display Credentials
Outbound delivery credentials displayed for the new mailbox. Mailbox is immediately active for send and receive.
Free Tier
- @calistopro.com address included
- Storage-capped mailbox
- Full feature access
Custom Domain
- Any verified domain from Sites
- 10 GB storage per mailbox
- Domain authentication key generation per domain
- MX and authentication records auto-setup
High-Performance Ops. Zero Monthly Overhead.
Get all 15 Core modules at no monthly cost. You only pay 2% of processed revenue.