Why Outbound AI Calls Get Flagged as Spam Likely, and How We Prevent It

Your outbound AI agent might be getting blocked, and you'd have no idea.

Picture it. A great script, a great voice, a clean list of leads. You launch the campaign and nobody picks up. You blame the offer. It's not the offer.

What's actually happening

The phone carriers are marking your number as "spam likely." You've seen that label on your own phone. Your leads see it too, and they never answer. Sometimes the call gets blocked before it even rings.

Out of the box, most new numbers will be marked as spam. You can check yours on a site like Nomorobo or IPQualityScore. If you're already running outbound, that check is worth doing today.

The two settings most people skip

Verified phone number. This tells the carriers your number is legit, not a robocall. On Retell it means submitting a business profile, and once it's approved your number loses that spam likely label when it calls people.

Branded call. This shows your business name on the screen when you ring, instead of a random number. One catch: Verizon cuts your business name at 15 characters, while T-Mobile and AT&T give you 32. Even "Oceanside AI Solutions" gets chopped on Verizon. Keep the name short.

Retell also requires an ID verification on the account before you run batch calls, so that's part of our setup too.

Concurrency and calls per second

I wish those add ons were all it took. There's one more piece, and if you don't understand it you're likely to overspend and have your numbers blocked without knowing why.

Concurrency is how many calls happen at the same time. Retell caps you at 20 by default across all your agents, and extra slots are $8 each per month. This matters because outbound and inbound share that pool. If your outbound campaign eats all 20, the agent answering your inbound calls can get choked out, so we reserve capacity for it.

Calls per second is how fast new calls get started. Picture a swimming pool: concurrency is how much water the pool holds, and calls per second is the faucet filling it. The default is one call per second. Here's where people get burned: if you pay for 100 concurrent calls but you're starting one call per second and each call averages 30 seconds, you'll only ever have about 30 going at once. You paid for capacity you can't use.

You can raise calls per second, up to 5 on Twilio and 16 on Telnyx. Retell recommends raising it gradually, because a sudden jump can get your number blocked. That's also why Twilio is fine to start, but Telnyx is better for large scale outbound.

Lists versus live triggers

There are two ways we set up outbound calling. Batch calling is for when you have a list. You upload it with the details you want the agent to use, like each lead's first name, and schedule the campaign to run on its own, say Monday morning. The time it takes is simple math: number of leads, divided by concurrency, times the average call length. Five leads, one at a time, at 5 minutes each is 25 minutes.

API calling is for when something happens and you need to react immediately. Someone fills out a quote form, a lead moves to a new stage in your CRM, and the call fires from your own system right away. That's how speed to lead works.

Either way, we turn on voicemail detection so the agent either hangs up or leaves a short message instead of talking to a machine.

Outbound is only worth running if people pick up. So before anyone obsesses over the script, make sure your number isn't flagged.