Invoice sending: returned emails and bounces

Overview

If an invoice email cannot be delivered, the recipient's mail server rejects it as a "bounce" (a returned email). This article explains how to recognize bounces and how to deal with them.

What is a bounce?

A bounce is an error message that comes back from the recipient's mail server when an email cannot be delivered. There are two types:

Hard bounce (error on the recipient's side):

• The mailbox does not exist or has been deleted
• The email address is invalid (e.g. syntax error)
• The recipient's server permanently rejects emails from the sender

Soft bounce (temporary error):

• The recipient's mailbox is full
• The recipient's mail server is temporarily unreachable
• The mail server rejects the email for temporary reasons

Recognizing bounces

In the web interface

1. Open the invoice details
2. Look for the "Deliveries" section
3. Look out for error messages or status information
4. The email address may be marked with an error indicator

Bounce notifications

If you have configured your own SMTP server, you may receive bounce emails from your mail server:

• Check your mailbox for NDRs (non-delivery reports)
• These contain errors from the recipient's server
• Note down the problematic email addresses

Checking via the API

Use GET /invoices/{faktooraId}/status to check the delivery history:

{
  "delivery": [
    {
      "type": "email",
      "recipient": "ungueltig@beispiel.de"
    }
  ]
}

Note: standard email deliveries do not store error status values. If a bounce has occurred, it may only be shown by bounce emails from your mail service.

Dealing with bounces

Fixing hard bounces

Step 1: Identify the recipient

• Note down the email address from the bounce
• Check whether you entered the address correctly

Step 2: Contact the recipient

• Call the recipient or contact them through another channel
• Ask for the correct email address
• Check whether the person still works for the company

Step 3: Correct the address

• Update the email address in faktoora
• Send the invoice again

Step 4: Clean up past records

• Check other invoices to the same recipient
• Correct the email address there as well where necessary

Fixing soft bounces

For temporary errors (mailbox full, server unreachable):

Step 1: Wait

• Soft bounces are usually temporary
• The recipient's server usually tries to deliver the email later

Step 2: Resend manually

• Wait a few hours
• Send the invoice again
• Check whether delivery succeeds this time

Step 3: Clarify with the recipient

• If several soft bounces occur, contact the recipient
• Ask them to empty their mailbox or check their system

Spam filters and blocking

Some bounces are not caused by real errors, but by spam filters or mail server blocking.

Signs:

• A bounce code such as 550 Rejected or 554 Service not available
• The recipient's server blocks emails from your domain
• The email is accepted but not delivered (it ends up in the recipient's spam folder)

How to fix it:

On your side:

• Check whether your domain is on blacklists
• Configure SPF and DKIM records correctly (if you use your own SMTP server)
• Make sure your IP address is not on spam lists

On the recipient's side:

• The recipient should clarify the matter with their IT team
• The recipient should mark faktoora emails as trusted
• The recipient should configure SPF or DKIM validation (if applicable)

Systems and automated recipients

Sometimes automated systems (e.g. SAP, ERP systems) cannot process the invoice email.

Common problems:

• Invalid format: the system does not recognize the invoice format
• Missing information: required fields are not present
• Attachments too large: the system rejects attachments above a size limit
• Invalid character encoding: UTF-8 or other encodings are not supported

How to fix it:

1. Contact the system administrator
2. Ask about the system's requirements:
   • Which file formats are supported?
   • Which encoding is expected?
   • Which email headers or metadata are required?
3. Adapt your invoices to the requirements
4. Send a test example and ask for confirmation

Sending with your own SMTP server

If you have configured your own SMTP server, you can track bounces in more detail:

1. Check your mail server's logs
2. Look for bounce notifications (NDR, Undeliverable)
3. Note down the exact error codes from the recipient's server
4. Contact faktoora support with the error details

See also: Setting up SMTP and sending

Best practices for minimizing bounces

1. Check addresses

   • Validate email addresses when entering them
   • Ask for confirmation of unusual addresses

2. Clean up regularly

   • Check old contacts for invalid addresses
   • Update recipient information as needed

3. Communicate with recipients

   • Let recipients know that they should expect invoice emails from faktoora
   • Ask them to add the address to their trusted senders

4. Optimize the SMTP configuration

   • If you use your own SMTP server, make sure SPF, DKIM and other authentication mechanisms are configured correctly
   • See: Setting up SMTP and sending