Phil Portman is a serial entrepreneur and the Founder & CEO of Textdrip — a small business SMS marketing tool to automate SMS campaigns.
I run an SMS marketing company, and almost every week someone calls me in a panic. Their texts stopped being sent, the campaign got flagged or the number was suspended overnight without any warning. It may be hard to believe, but every time the reason is the same: A2P 10DLC.
Most business owners have never heard this term, and very few understand it. However, if you send even one automated text message to a customer, these rules already apply to you. And if you break it, you don’t get a warning letter, but your message gets blocked.
Here are some of the most common A2P 10DLC mistakes I see. However, before diving deep into those mistakes, let’s first understand what A2P 10DLC is.
What Is A2P 10DLC?
A2P 10DLC stands for “application-to-person” messaging on 10-digit long codes. It is the system that carriers like AT&T, Verizon and T-Mobile use to check who is texting their customers and why.
Before A2P 10DLC existed, anyone could blast mass texts from a regular-looking phone number, but as spam messaging increased, carriers built a registry. Now, every business must register its brand and declare exactly what kind of messages it plans to send. If you skip registration, your texts don’t get delayed, but they get blocked. Even Twilio’s documentation confirms it: Any message from a 10DLC number not tied to an approved campaign gets rejected overnight and returns error code 30034. Unregistered traffic incurs additional per-message carrier surcharges.
Don’t Treat Registration As The Final Stage
Understand that registering your brand and campaign is only the first step, not the whole job. But I have seen founders who register once, get approved and assume they’re covered forever. The reality is that they’re not.
These days, carriers use AI to compare your live message against the sample you submitted at registration, and “even compliant campaigns can be filtered if traffic patterns raise flags.”
If you don’t send for what you registered, your traffic throttles. Your delivery rate drops. According to Twilio’s penalty guidelines, for content issues like phishing, you need to pay a fine of up to $2,000 per violation. Brands registered in 2023 or 2024 may need to reverify because outdated registrations are a common filtering trigger today.
To fix this, keep sending what you said you would send and update your registration when your business changes. Now, let’s understand what mistakes most business owners make.
Never Mix Marketing Into Service Texts
This one is the biggest reason why campaigns get rejected or shut down. For example, you send an appointment reminder text and then add, “By the way, refer a friend and get $20 off.” That one line turns the entire message into marketing under carrier rules and the law.
If that message was not registered as marketing, you are in violation. You won’t find out about this by any email or warning message, but you will find out when your mobile carrier suspends your messaging lines. Therefore, always keep your lanes separate. Transactional must remain transactional, and marketing should run through its own registered campaign with its own opt-in.
Never Ignore Quiet Hours And Opt-Outs
This is most common, but I still see it constantly. You can’t text customers before 8:00 a.m. or after 9:00 p.m. in their local time zone. So, if your customers span states, your sending schedule needs to account for that.
The same goes for STOP replies. If you keep messaging someone even after they request to opt out, you will face violations with financial penalties. If someone requests opt-outs, it must be honored immediately. Even this bar is rising at the state level, too. Virginia’s SB 1339 has been in effect since January 2026, and under it, businesses must honor a text opt-out for a full 10 years. Even Texas has expanded its telemarketing law to explicitly cover texts.
Avoid Buying Phone Number Lists
I understand the temptation. Growth is hard, and a list of 10,000 customers looks like a shortcut, but in reality, it is a liability. Also, customers who gave their numbers do not automatically mean they agreed to receive texts from you. That’s why documenting proper consent is essential. A smaller list of people who actually want texts from you is more valuable than a huge list of people who never asked for them.
Purchased lead lists inherit every consent defect of whoever collected them. If you can’t prove a customer agreed to hear from your business, you can’t protect your brand from violations.
Keep The Brand Name Consistent
If the brand name customers see does not match what you registered with the carrier, your messages get flagged as spam. It is common with agencies texting on behalf of clients under a different display name. Keep your registered brand, website and customer-facing name consistent.
Why A2P 10DLC Compliance Matters
Texting is one of the highest-performing channels for a business, with a 98% open rate and a 45% response rate. But that advantage only exists if your messages actually arrive. Every business I’ve watched get burned didn’t break these rules on purpose. They just didn’t know the rules existed. But the fact is, ignorance doesn’t protect you from a carrier suspension or from regulators. So, compliance matters for businesses.
What To Do To Stay Compliant
Audit your SMS campaigns against what you actually registered. Separate promotional texts from service texts. Check that your opt-out process works end to end. Confirm your sending hours respect every time zone your customers live in. And validate your phone number lists. All these require just 10 minutes!
A2P 10DLC compliance looks technical, but underneath everything, its principle is simple: If someone gives you permission to text them, respect that permission. If they take it away, respect that, too.
The businesses that win with SMS won’t be the ones sending the most texts. They’ll be the ones whose texts actually arrive because they never gave a carrier a reason to block them.
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