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Every email needs a sender and at least one recipient, but transactional emails often involve more complex addressing — copying a manager on an order confirmation, blind-copying a compliance archive, or routing replies to a support team instead of a no-reply address. Lettr gives you full control over To, CC, BCC, Reply-To, and sender display names.

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To Recipients

Send to one or multiple recipients: 
// Single recipient
await lettr.emails.send({
  from: 'you@example.com',
  to: ['recipient@example.com'],
  subject: 'Hello',
  html: '<p>Hello!</p>'
});

// Multiple recipients (up to 50)
await lettr.emails.send({
  from: 'you@example.com',
  to: ['alice@example.com', 'bob@example.com', 'carol@example.com'],
  subject: 'Team Update',
  html: '<p>Hello team!</p>'
});

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CC Recipients

CC recipients receive a copy of the email and are visible to all other recipients. Use CC when transparency matters — for example, copying a manager on a project update or keeping a team lead informed about client communications. 
await lettr.emails.send({
  from: 'you@example.com',
  to: ['primary@example.com'],
  cc: ['manager@example.com', 'team-lead@example.com'],
  subject: 'Project Update',
  html: '<p>Here is the latest update...</p>'
});

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BCC Recipients

BCC recipients receive a copy of the email but are hidden from all other recipients. Common uses include compliance archiving (sending a copy to a records system), internal monitoring (copying a sales pipeline tool), or sending to multiple customers who shouldn’t see each other’s addresses. 
await lettr.emails.send({
  from: 'you@example.com',
  to: ['customer@example.com'],
  bcc: ['sales-archive@example.com', 'compliance@example.com'],
  subject: 'Your Order Confirmation',
  html: '<p>Thank you for your order!</p>'
});

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Reply-To Address

Reply-To lets you send from one address (like noreply@example.com) while directing replies to another (like support@example.com). This is useful when your sending address is automated but you want replies to reach a real team. 
await lettr.emails.send({
  from: 'noreply@example.com',
  from_name: 'Acme Support',
  to: ['customer@example.com'],
  reply_to: 'support@example.com',
  reply_to_name: 'Acme Support Team',
  subject: 'Your Support Ticket',
  html: '<p>We received your request...</p>'
});

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Sender Name

The from_name parameter sets the display name that appears alongside the sender’s email address in the recipient’s inbox. A clear, recognizable sender name improves open rates because recipients can identify who the email is from before reading the subject line: 
await lettr.emails.send({
  from: 'notifications@example.com',
  from_name: 'Acme Inc',
  to: ['recipient@example.com'],
  subject: 'Welcome to Acme',
  html: '<p>Welcome aboard!</p>'
});
The recipient will see: Acme Inc <notifications@example.com>

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Recipient Limits

LimitValue
Max recipients per request50 (combined to, cc, bcc)
Max email address length255 characters
Sending to more than 50 recipients requires multiple API calls. For bulk sending, see Batch Sending.

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Email Address Validation

Lettr validates all email addresses before accepting a send request. Each address must pass three checks:
  • RFC 5322 format — The address must conform to standard email format
  • Valid DNS records — The domain must have DNS records that accept email
  • Not suppressed — The address must not appear on your account’s suppression list
If any address fails validation, the API rejects the request and the email is not sent to any recipient: 
// Invalid email format
{
  "error_code": "validation_error",
  "message": "The given data was invalid.",
  "errors": {
    "to.0": ["The to.0 must be a valid email address."]
  }
}

// Too many recipients
{
  "error_code": "validation_error",
  "message": "The given data was invalid.",
  "errors": {
    "to": ["The to field must not have more than 50 items."]
  }
}

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Combined Example

Here’s a realistic example that uses multiple recipient features together — an order confirmation sent to the customer, CC’d to their account manager, BCC’d to the order archive, with replies directed to the support team: 
await lettr.emails.send({
  from: 'orders@yourstore.com',
  from_name: 'YourStore',
  to: ['customer@example.com'],
  cc: ['account-manager@yourstore.com'],
  bcc: ['order-archive@yourstore.com'],
  reply_to: 'support@yourstore.com',
  reply_to_name: 'YourStore Support',
  subject: 'Order #12345 Confirmed',
  html: '<p>Thank you for your order! Your items will ship within 2 business days.</p>'
});

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Recipient Parameters Reference

ParameterTypeRequiredDescription
tostring[]YesPrimary recipient(s)
ccstring[]NoCarbon copy recipients
bccstring[]NoBlind carbon copy recipients
fromstringYesSender email (must be from verified domain)
from_namestringNoSender display name
reply_tostringNoReply-to email address
reply_to_namestringNoReply-to display name