Your own SMTP

Connecting your own SMTP server lets Free Invoice Automation send your invoices, estimates, receipts and reminders from your own email address, through your own mail server. Your clients see your address, replies land in your inbox, and the sends never count against the platform email allowance. This is the way to send more than 20 emails a month on Free or 100 on Team.

How it works

Your SMTP mailbox is a sender connection on a business. Once it is connected and verified, it becomes that business's default sender, and every email for that business goes through it unless a client or a document says otherwise.

The sender for each email is resolved in this order:

1. A sender set on the document.
2. The client's preferred sender.
3. The business default sender (your SMTP once connected).
4. Platform email, only if the account still has quota left.

Because a sender connection belongs to a business, each business can send from its own mailbox. If you run two businesses, connect one SMTP mailbox to each.

No monthly limit from us

Emails sent through your own SMTP have no monthly quota on any plan. Your mail provider may have its own sending limits, and those still apply. On Free, the general fair-use limits on sends per minute also apply to protect the service.

What you need

From your email provider or hosting control panel, collect your mailbox's SMTP details:

• the SMTP host name;
• the port: 25, 465, 587 or 2525;
• the username (often the full email address);
• the password (or an app password, if your provider uses them).

Connect SMTP in the web app

Connect SMTP through the API

A sender connection is created with Create a connection, with kind: "sender" and provider: "smtp". The exact fields come from the smtp sender's connection schema, listed on the endpoint page. The password is accepted on write and never returned.

curl -X POST "https://api.freeinvoiceautomation.com/v1/connections" \
  -H "Authorization: Bearer $FIA_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: smtp-acme-studio" \
  -d '{
    "business_id": "0193f2a1-7c4e-7b9a-9f10-3c2d1e0a4b51",
    "kind": "sender",
    "provider": "smtp",
    "label": "Acme Studio mailbox",
    "host": "smtp.example.com",
    "port": 587,
    "username": "[email protected]",
    "password": "app-password-here"
  }'

Then use Verify a connection to run the handshake again at any time, Update a connection to change the details, and Delete a connection to remove it. List connections shows each sender with its status.

SMTP connections are not managed over MCP. Your assistant still sends through them: when it calls send_document, the same sender resolution picks your SMTP mailbox.

Connection status

We re-check connections every night. If your connection starts failing, update the password or settings and verify again. Each failed send is recorded in the message log with its error, so you can see which emails did not go out.

Security

Your SMTP password is a secret, and it is treated like one:

• It is sealed (encrypted) as soon as it reaches us, is write-only (no screen or API call ever shows it again, only the last few characters for recognition) and is never written to logs.
• An SSRF guard checks the host before we connect. Private, loopback, link-local and other internal network addresses are blocked, we connect to the exact address that was checked, and only the SMTP ports 25, 465, 587 and 2525 are allowed. This stops anyone from using the SMTP form to reach systems inside our network.
• Connection attempts use short timeouts.

Your own mail server is outside our control. Its security, deliverability and limits are between you and your mail provider.

Rules and edge cases

• One send per event. Each send is unique per document, event and channel, so a retried or double-clicked send never emails your client twice.
• Per business. A connection belongs to one business. Members who can reach that business send through it according to their permissions; they never see the password.
• Overrides. You can set a different sender for a single client or a single document, for example to send one client's invoices from a different mailbox.
• No "Powered by" changes. The email footer follows your plan's branding, whichever sender is used.
• Deliverability. Mail from your own server is sent under your own domain's reputation. If emails land in spam, ask your provider about SPF, DKIM and DMARC for your domain.

Errors

See Errors for the error shape.

Permissions

By default only Owner and Admin have senders.manage. See Roles and permissions.

Related pages