Your subject lines in collection emails make a huge difference in whether your customer will pay on their invoice. The invoice, payment reminder, and final collection email subject lines are the very first thing they see that will get their attention. Your subject lines can also trigger whether the email will even make it into their inbox, past their spam folder. Thinking like a marketer when sending these emails will help to craft a catchy subject line that is sure to get the customer to open the email and take action. We took a few tips from the marketer’s playbook that you can apply to your collection emails.


There are some words that you should never use in your collection email subject lines because they will automatically trigger the spam filters. Spam filters have become much more sophisticated. Since so many fake emails pertaining to money no make it into our inbox, there are many words you may be using in regards to invoices that are automatically being flagged as spam.

Below is a list of words and characters you should always try to avoid.

  • Money
  • $
  • Cash
  • Check
  • Credit
  • Credit bureaus
  • Discount
  • Price
  • Accept Credit Cards
  • Avoid
  • Act Now
  • Call now
  • Don’t delete
  • Don’t hesitate
  • Now
  • Please read


After reading the above list of words not to use, you may be wondering what you could even use in your subject line that will make it catchy enough for a customer to open. The main point you want to get across to your customer, even if you are sending a mass email blast with AR software, is that the email directly effects them. Studies have shown that putting a customer’s account number or invoice number in the subject line can help them to open the email. You can also try to ask the customer a question in your follow up reminder email, such as have they seen this past due invoice?


Sometimes it can be hard to come up with subject lines that fall within these constraints on your own. Below we’ve included some subject line examples you can try.

  • Invoice for Account Number 1234
  • Payment Needed for Invoice Number 1234
  • Account Number 1234 Payment Needed
  • Have You Seen This Past Due Invoice?
  • Have You Paid Invoice Number 1234?

You don’t have to stick with creating one “perfect” subject line, either. Many marketers test subject lines and see which ones work the best. Try out a couple different ones and find the one that works best. Using the same subject line over and over can also cause your customer to lose interest, so switching it up can also be beneficial to ensure your customer takes action and pays.