Manage DSO with a 5-stage dunning process, email templates, and automation tips that preserve customer relationships and speed up payments.
Most businesses lose money the same way. They send the invoice, they wait, and no oney follows up. The customer is not refusing to pay. The customer just has fifty other invoices in their inbox, and yours is not on top of the stack.
A dunning letter can ehlp. It is a structured communication that walks an unpaid invoice through stages of escalation, from a friendly reminder to a final demand. Done well, it protects cash flow, lowers DSO, and keeps customer relationships intact. Done poorly, receivables age and good customers drift into bad-payer behavior.
This guide is written for SMB controllers, AR managers, bookkeepers, and accounting firms managing receivables across multiple clients.
A dunning letter is a written notice (usually email) sent to a customer to request payment on an overdue invoice. The word comes from the 17th-century English verb "to dun," meaning to demand repayment of a debt. Per Investopedia, modern dunning is the methodical communication businesses use to ensure collection of receivables, with messaging that escalates as accounts age.
Inconsistent follow-up can train customers to pay late. If you follow up on one of your invoices but didn’t communicate about three others did not, they reasonably conclude that yours is not the one to pay first.
A dunning process replaces ad-hoc emails with a system. Each stage has a defined trigger, message, and next action. The shift from "we get to it when we get to it" to "every invoice follows the same predictable path" is what reduces days sales outstanding (DSO) faster than any tone change ever will.
The process is firm. The tone stays respectful.
These three terms get used interchangeably, but they describe different stages. A payment reminder is a low-friction notice, usually pre-due or just past-due, that assumes oversight. A dunning letter is the broader category covering all stages of structured communication, from polite reminder through final demand. A collection letter is the language used at firm-notice and final-demand stages, referencing prior communication and introducing consequences. Aligning your team on which term applies at which stage prevents mixed signals to customers.
Dunning sits at the receivables end of order-to-cash, but the work that determines whether it succeeds happens upstream. Invoice accuracy, delivery confirmation, payment options, and a clear dispute path all shape how often you will need to escalate. The accounts receivable process end to end is the foundation. The International Federation of Accountants (IFAC) frames this as systematic credit control: expectations set at engagement and reinforced through consistent process.
Timing matters less than what you confirm before the timer starts. If the invoice never arrived or is wrong, no amount of polite escalation will get it paid faster.
Before the first reminder goes out, confirm:
Skipping this checklist is how AR teams end up sending firm notices to customers who say, with full justification, "We never got the invoice."
The communication cadence should be based on days past due plus customer segment. A reasonable default starts with a pre-due reminder 3 to 5 days before the due date and escalates through five stages from 1 to 60+ days past due (full schedule below).
Overdue invoices are baseline in B2B credit relationships. According to the 2025 Atradius Payment Practices Barometer, 43% of credit-based B2B sales in the US and 44% in Canada are currently overdue, with roughly 5% to 6% of long-outstanding invoices written off as bad debt.
The hardest part is deciding in advance what triggers a final demand and what happens after:
Once written, this policy travels with every customer file. Without it, every late account becomes a fresh debate.
The default 5-stage cadence gives the customer multiple low-friction chances to resolve before tone or terms shift. Each stage has a job. Get the rhythm right and most invoices are paid by stage 2 or 3.
| Dunning stage | Typical days past due | Primary goal | Tone | Suggested subject line | Must-include elements | Next action if unpaid |
| Stage 1: Reminder | 1 to 3 | Prompt fast payment | Warm, helpful | Reminder: Invoice #___ due on ___ | Invoice link, amount, due date, pay options | Auto-send Stage 2 |
| Stage 2: Polite nudge | 7 to 10 | Get a commitment date | Direct, courteous | Past due: Invoice #___ payment status? | Request ETA, confirm no issues, point of contact | Task for call + Stage 3 |
| Stage 3: Firm notice | 14 to 21 | Set a deadline | Firm, neutral | Action required: Invoice #___ now ___ days overdue | Deadline, consequences, dispute path | Suspend terms, send Stage 4 |
| Stage 4: Final demand | 30+ | Final internal attempt | Strong, professional | Final notice: Invoice #___ must be paid by ___ | Final date, consequences, escalation contact | Stage 5 |
| Stage 5: Pre-collections | 45 to 60+ | Prepare referral or hold | Formal | Notice of intent to refer or apply account action | Referral timeline, documentation request | Refer or place hold |
A flat cadence across every account is the second-most-common collections mistake (after no cadence at all). Segment first, then tune:
Accounting firms can build these segments once at the firm level, then tune by client. This is where templated, multi-tenant AR workflows save hours per week per controller.
Every dunning email follows the same format:.
The variable is tone. Below are templates you can useas a starting frame and match wording to your brand and customer segment.
Subject: Reminder: Invoice #1042 due [date]
Hi [Name],
Quick note that invoice #1042 for $[amount] was due on [date]. If it has already been paid or scheduled, please disregard this note. If not, you can pay using the link below or reply to this email and we will help.
[Pay invoice link]
Thanks, [Sender]
You’re assuming that oversight is the cause, and friction is minimal. Most invoices can be resolved here.
Subject: Past due: Invoice #1042 payment status?
Hi [Name],
Following up on invoice #1042 for $[amount], which is now [X] days past due. Could you confirm one of the following:
[Pay invoice link]
Looking forward to your reply.
[Sender]
This is still collaborative, but asking for a commitment, which gives you something to follow up on at stage 3.
Subject: Action required: Invoice #1042 is now [X] days overdue
[Name],
Invoice #1042 for $[amount] was due [date] and is now [X] days past due. We sent reminders on [date 1] and [date 2] and have not received a response.
Please remit payment by [deadline] or contact [escalation name] at [email] to discuss payment terms or any dispute. If we do not hear from you by [deadline], the account will be subject to [consequence: e.g., suspension of services, removal of credit terms, late fees].
[Pay invoice link]
[Sender]
This tone shifts to neutral and factual, referencing prior communication with dates. Introduce a concrete deadline and consequence to keep the dispute path open.
Subject: Final notice: Invoice #1042 must be paid by [date]
[Name],
This is a final notice on invoice #1042 for $[amount], originally due [date], now [X] days past due. We have sent prior notices on [dates] and have not received payment or a response.
Payment must be received by [final deadline] to avoid [consequence: e.g., account suspension, account hold, referral to a third-party collections partner]. We would prefer to resolve this directly. If there is a dispute or hardship issue, please contact [escalation name] at [email] before [deadline].
[Pay invoice link]
[Sender]
At this point, your communication is short, formal, and references specific dates and consequences. The "we want to resolve this directly" framing keeps the door open without softening the deadline.
Subject: Notice of intent to refer to collections (or place account on hold)
[Name],
Despite multiple notices dated [list], invoice #1042 for $[amount] remains unpaid. Effective [date], the account will be referred to a third-party collections partner, placed on hold, or submitted for credit-term review (whichever applies per your policy).
If you intend to dispute this balance or submit documentation, you must do so by [date]. After that date, the account will proceed as outlined.
[Sender]
Here you remain formal, straightforward, with no inflammatory language. Notice of what will happen, date by which the customer can still respond, documentation cue.
A few best practices to follow:
If you are not sure whether your collections process is working, the symptoms tend to cluster in three places.
If three or more of these apply, the process is the problem, not the customers.
Most teams know they should automate. The question is what they actually gain.
| Capability | Manual dunning | Automated dunning (AR collections software) |
| Timing consistency | Depends on memory and calendars | Rules-based, always-on cadence |
| Personalization at scale | Hard. Copy-paste risk. | Templates plus dynamic fields plus segmentation |
| Audit trail | Scattered across inboxes | Centralized communication history |
| Team collaboration | Hard to see who contacted whom | Shared timeline and ownership |
| Promise-to-pay handling | Spreadsheet tracking | Automated pause and restart logic |
| Escalation control | Inconsistent tone and stages | Standardized stages with approvals |
| Reporting | Lagging and manual | Real-time stage conversion and DSO impact |
| Customer experience | Variable | Predictable, professional, on-brand |
Automation is the floor, not the ceiling. It does not replace strategic phone calls for high-risk or high-value accounts, dispute resolution, or relationship management with key accounts. Automation handles the volume so humans can handle the exceptions.
Most invoices get resolved in the first two stages, which is where automation pays back fastest: faster early-stage recovery, fewer "lost" invoices, cleaner handoffs to leadership when escalation is genuinely needed. With baseline overdue rates at 43% in the US and 44% in Canada per Atradius, the question is not whether to automate. It is how much DSO drift you can absorb before you do.
Automation amplifies what you configure. If your policy is muddled, the automation will be too. Build in this order:
The reporting layer is what separates "we sent reminders" from "DSO dropped eight days quarter over quarter and here is which segment drove it."
Plooto sits between accounting software and the bank as your accounts receivable layer for SMBs and accounting firms. For dunning specifically, that means scheduled reminders, automated follow-ups, and centralized visibility, all in one workflow.
Three things matter day to day:
The system runs the cadence. The team focuses on exceptions, disputes, and high-value relationships. Walk through how this looks inside accounts receivable automation software.
If you are not sure where to start, the lowest-risk pattern is:
That covers the bulk of the volume on day one and lets you tune the harder stages over the next quarter.
The implementation question is not just "what do we automate." It is "who owns this."
In an SMB, the controller or AR manager owns policy and finance executes. Sales is aligned but does not run the process.
In an accounting firm, the partner or practice manager defines a standard framework. Each client gets specific tuning: terms, tone, escalation contacts, brand voice. The firm-level framework is the asset that scales across the book of business. Without it, every new client adds bespoke setup hours.
The cheapest dunning is the one you never need to send. Set expectations at onboarding: payment terms and remittance instructions in writing, confirmation that the AP contact is correct, a pre-due reminder by default. A working pay link, invoice templates that match what AP teams expect to see, and a clean remittance capture mechanism do more for DSO than any subject-line variant.
Plan escalation before you need it. Decide when the account manager gets involved versus the finance lead, when terms shift (NET 30 to due-on-receipt, deposit-required, autopay), and when service pauses. These decisions are easier in calm than in crisis.
Keep an audit trail. Every notice, every response, every commitment. If any portion of your collections is consumer-facing, consult counsel on FDCPA and Reg F applicability before going live with AR automation. For B2B-only AR, the documentation discipline still pays off the first time a customer disputes a balance and you can pull the entire history in two clicks.
The 5-stage cadence is the simplest version of what works: reminder, nudge, firm notice, final demand, pre-collections. The biggest lever is not tone or template wording. It is consistency. Customers pay the businesses that follow up the same way every time, and they let the others wait.
Three actions to take this week:
Once policy is set, walk through Plooto pricing to see which plan fits the receivables volume you are managing today and where you expect to be in twelve months.