I'm building a Python app and need an API to send invoices by email

If you want to send invoices by email from a Python app, the simplest approach is usually:

1. Generate the invoice as a PDF
2. Email it as an attachment using an email provider API or SMTP
3. Optionally track delivery/open status

Good API options

1. SendGrid

• Easy to use from Python
• Good for transactional email
• Supports attachments, templates, analytics

2. Mailgun

• Great for transactional email
• Simple HTTP API
• Good deliverability

3. Amazon SES

• Very cost-effective
• More setup, but scalable
• Good if you already use AWS

4. Postmark

• Very good for transactional emails
• Simple API and strong deliverability

Recommended stack for invoice emails

• PDF generation: reportlab, WeasyPrint, or wkhtmltopdf
• Email sending: SendGrid / Mailgun / SES
• Optional storage: S3 or similar for invoice PDFs

Example: SendGrid in Python

import base64
from sendgrid import SendGridAPIClient
from sendgrid.helpers.mail import Mail, Email, To, Content, Attachment, FileContent, FileName, FileType, Disposition

message = Mail(
    from_email=Email("billing@yourcompany.com"),
    to_emails=To("customer@example.com"),
    subject="Your Invoice #12345",
    plain_text_content=Content(
        "text/plain",
        "Hi, please find your invoice attached."
    )
)

with open("invoice-12345.pdf", "rb") as f:
    encoded_file = base64.b64encode(f.read()).decode()

attachment = Attachment(
    FileContent(encoded_file),
    FileName("invoice-12345.pdf"),
    FileType("application/pdf"),
    Disposition("attachment")
)

message.attachment = attachment

sg = SendGridAPIClient("YOUR_SENDGRID_API_KEY")
response = sg.send(message)
print(response.status_code)

Things to consider

• Make sure your invoices are properly branded and compliant
• Use a verified sender domain
• Add error handling and retries
• Store invoice metadata in your DB
• If invoices contain sensitive info, ensure:
  • HTTPS
  • secure API key storage
  • access control
  • possibly password-protected PDFs

If you want the easiest recommendation

• SendGrid or Postmark for simplicity
• Amazon SES if cost is most important

If you want, I can also give you:

1. a full Python example,
2. a FastAPI endpoint for sending invoices,
3. or a comparison table of SendGrid vs SES vs Mailgun vs Postmark.