Skip to main content
A mailbox is one email address on a verified sending & receiving custom domain or on the shared myagent.mx domain. It can send mail, receive mail, hold messages, and have its own passwords and sender rules.
Each team starts with 50 active mailboxes. See Team limits.

​
Create a mailbox

1

Open Mailboxes

Open Mailboxes and select Create mailbox.
2

Choose the address

Enter a local part and choose a verified sending & receiving domain. Leave the local part blank if you want Sendmux to generate one.
3

Set display name and storage

Add an optional display name and choose 1 GB, 5 GB, or 50 GB storage.
4

Save the password

Copy the mailbox password when it appears. It is shown once.

​
Mailbox passwords

Create one password per device, app, or integration. That makes revocation safer because you can remove one password without breaking every other connection. Mailbox passwords can be used for:
  • Sending through SMTP.
  • Authenticating mailbox-scoped API calls.
  • Connecting a mail client to the mailbox.
Use New password on the mailbox detail page to create another password. Use Revoke to disable one immediately.

​
Send from a mailbox

Use a mailbox password as the SMTP password or as the bearer token for the Sending API. For mailbox-style workflows, call POST /mailbox/messages/send through the Mailbox API to send as the authenticated mailbox and track its submissions.

​
Sender identity

Open a mailbox and choose Edit sender identity to set:
  • Sender name.
  • Plain text signature.
  • HTML signature.
These values become the mailbox defaults. Individual API sends can still provide their own message fields.

​
Sender rules

Sender rules control inbound mail for the mailbox. Open a mailbox and use the Sender rules card to add rules, then choose Save rules. A mailbox can use allow rules or block rules, not both at the same time. Clear all rules before switching rule type. Removing every rule turns filtering off, so all senders are delivered again.

​
Pattern formats

Each rule matches the sender’s envelope address. Three formats are accepted: Patterns are case-insensitive and stored in lowercase. Each rule can carry an optional note (up to 255 characters) to record why it exists — notes never affect matching. A mailbox or domain can hold up to 1,000 rules.

​
How matching works

  • Rules run before a message is accepted, so a blocked sender receives a rejection from their own provider rather than landing in spam. Rejected mail is not billed as accepted inbound usage.
  • Mailbox rules take precedence: when a mailbox has its own rules, any domain-wide rules are skipped for that mailbox.
  • If a rule can’t be saved, the editor shows the reason inline — fix the highlighted pattern and save again.

​
Manage rules via the API

The Management API exposes the same rules for automation: GET/PUT /mailboxes/{public_id}/filters for one mailbox, and GET/PUT /domains/{public_id}/filters to apply a rule set across every mailbox on a sending & receiving domain. Each PUT replaces the whole rule set in a single atomic operation. See the Management API reference.

​
Suspend, resume, and delete

  • Suspend pauses inbound mail, outbound sends, mailbox API access, IMAP, and SMTP without deleting messages, passwords, or settings.
  • Resume restores mailbox access and sending from the mailbox address.
  • Delete removes the mailbox, its messages, API keys, and passwords.

Domains

Verify sending & receiving domains before creating branded mailboxes.

API keys

Create mailbox keys for API and mail client access.

Push delivery

Choose between polling, realtime events, webhooks, and the coming-soon push URL.

Webhooks

Receive inbound and delivery events at your HTTPS endpoint.

Mailbox API

Stream live received-message events from a mailbox key.