Most AR teams default to email for collections contact. It is the channel they use for everything else, it leaves a paper trail, and it is easy to send at scale. For many situations, email is the right choice. But the teams that improve their collection rates most significantly are the ones that stop treating email as the universal default and start treating channel selection as an actual decision that depends on the account and the situation.
The question is not which channel is best in aggregate. The question is which channel this specific customer actually responds to, given the current aging stage and the account relationship context.
What Email Does Well
Email works best for routine, current-due and early-overdue contacts to customers who process invoices through email-based AP workflows. These customers read their business email regularly, their AP team receives payment requests by email as a standard part of operations, and a properly formatted reminder with clear invoice details and a payment link is easy for them to action without escalation.
Email also creates a documentation trail that matters in some business contexts. If a customer later disputes that they received a reminder, email provides evidence. For businesses in regulated industries or with formal procurement processes, email contact at the right stages creates an audit trail that phone or SMS does not replicate as cleanly.
The limitation of email is attention. A business customer who receives 200 emails per day has a different relationship with their inbox than one who receives 40. In high-email-volume environments, an invoice reminder competes with internal communications, vendor notifications, and sales outreach. Even opened emails can be acknowledged mentally without being actioned. Email open rates tell you the message was received; they do not tell you the invoice will be paid.
When SMS Outperforms Email
SMS has a fundamental attention advantage over email in most business contexts: it is a less saturated channel for B2B communications, so a message stands out more prominently. Response rates to SMS for payment reminders tend to be meaningfully higher than email across most customer segments, particularly for contacts in the 15 to 45 day overdue window where getting a response to move the invoice forward matters.
SMS works best for customers who have given explicit consent to be contacted by text, and where the message can be kept short and direct: invoice reference, amount, and a payment link or a request to confirm receipt. Longer messages belong in email. SMS contact without prior relationship establishment can feel intrusive; it works best for customers who already know you and with whom the channel has been agreed in advance.
The practical constraint on SMS is that it requires having a mobile number for the right contact at the customer organization. In Japanese business contexts particularly, determining whether a business mobile number is appropriate to use for collections contact requires understanding the relationship and sometimes explicit confirmation. This is not a reason to avoid SMS, but it is a reason to build your SMS contact database carefully rather than using whatever number you happen to have on file.
When to Use the Phone
A phone call is a high-effort, high-attention channel. It interrupts what the customer is doing, requires a real-time response, and creates an interaction rather than a document. These properties make it the wrong channel for routine early-stage reminders, and the right channel when the situation has developed enough that you actually need a conversation.
Phone contact is appropriate in the 45-plus day range when email and SMS contacts have gone unanswered. It is appropriate when you need to understand why payment has not occurred: is there a dispute, a processing issue, or a financial problem that needs to be addressed? Email cannot answer those questions; a conversation can. And phone contact is appropriate for high-value accounts in the 30-60 day range where the relationship warrants a more personal contact than a digital message.
We are not suggesting that a human-placed phone call is always required. There is a useful middle ground in the form of phone-coaching prompts: structured notes that tell the AR team member who they are calling, what the account situation is, what questions to ask, and what outcome to try to produce from the call. The call still requires a human, but the preparation time is drastically reduced and the contact is more effective because the caller arrives informed.
Building a Channel Decision Framework
The way to operationalize channel selection without making it a case-by-case decision for every invoice is to define rules that map account and situation characteristics to channel choices. A simple framework has three dimensions: the aging stage of the invoice, the customer's historical response to previous channels, and the relationship tier of the account.
On aging stage alone: day 0-15 defaults to email; day 15-30 uses email with SMS escalation if no response within the expected window; day 30-60 uses SMS primary or phone if the customer has not responded to two digital contacts; 60-plus uses phone with human handling.
Customer response history overrides these defaults: if a customer who is 25 days overdue has a clear history of responding immediately to email but never to SMS, stay on email. If a customer who is 12 days overdue has never responded to email for any previous invoice but pays within 24 hours of an SMS, move to SMS immediately.
Account relationship tier sets the sensitivity floor: key accounts at any aging stage should have a human review the channel choice rather than following automatic rules, because the cost of a channel misstep with a major customer outweighs the efficiency gain.
The Channel Sequencing Mistake to Avoid
The most common channel error is sequential escalation on a fixed schedule regardless of response. Send email on day 7, then another email on day 21, then an email and SMS on day 45, then a phone call on day 60. The schedule is predictable and slow. A customer who ignores email will continue ignoring email regardless of how many times it arrives.
A better approach treats non-response to a channel within the expected response window as a signal to switch channels, not to resend on the same channel. If a customer with a 5-day typical email response time has not responded by day 8 after an email reminder, that is the moment to introduce a different channel, not to wait until day 21 for the next scheduled email. The goal is to find the channel that gets a response, not to cycle through a predetermined sequence.
