Blog Texting 6 min read
What is Sticky SMS and why your reply rate depends on it
By Wade, Duckrow's research duck. Updated .
The short answer
Sticky SMS means a lead always hears from the first number that texted them: every later step in the sequence and every reply your team sends goes out from that same number. It matters for replies because a text thread lives on one number. Keep the number and the lead keeps the context, the history and a sender they recognise. Change it and every message starts again as a stranger.
What is Sticky SMS?
Sticky SMS is a rule for teams that text from more than one number. The first time a lead gets a text, one number from your pool is pinned to that lead. From then on, every automated text in the sequence and every reply you send by hand uses the pinned number.
Volume still spreads across the pool, because each new lead can get a different number. What never changes is the number a given lead sees.
Why does the sending number affect your reply rate?
On a phone, a text conversation is grouped by the number it came from. Each new number opens a new thread with no history above it. That shapes how a lead reads your message.
- Recognition: a follow-up from the number they already know reads as the next line of a conversation. The same words from a new number read as a stranger getting in touch.
- Context: your earlier messages, and anything the lead wrote back, sit right above the new text when the number stays the same. On a new number, the lead has to remember who you are.
- Saved contacts: if the lead saved your number after the first text, later texts from that number show your name. Texts from any other number arrive unnamed.
A reply is a small act of trust. Every message that arrives as an unknown number asks for that trust from scratch.
What happens to replies when numbers rotate?
Rotation that picks a number for each message, instead of for each lead, causes three problems you can see in any inbox:
- Split threads: the lead answers step one on number A while step two has already gone out from number B. Now there are two conversations on their phone.
- Replies on the wrong line: your answer to their question comes from a different number than the one they texted, without the question above it.
- Lost follow-up: when replies spread across several numbers, it is easy for a team to miss one, or to answer it late.
None of this shows up as an error. It shows up as leads who go quiet.
How do different outbound tools choose the sending number?
Based on each vendor's own documentation, checked on 29 September and 1 October 2026:
| Tool | How the number is chosen | Text replies |
|---|---|---|
| Duckrow | Pinned to the lead on the first text, for every step and every reply | In the same inbox as email and LinkedIn |
| lemlist | You choose the sender on each SMS step | In lemlist's inbox |
| Reply.io | Its docs don't describe keeping a lead on one texting number | In a separate SMS Inbox |
| Instantly | Chosen for each one-off text from the CRM | In the CRM's own inbox |
How can you check your own setup?
- Pick ten leads who got more than one text and look at the numbers each one received. If any lead saw two numbers, rotation is per message.
- Find replies that came in on a number other than the one that sent the last text. Each one is a split thread.
- Check which number your team's manual replies go out from. It should be the number the lead texted.
- Check what happens when a number hits its daily limit. The lead should wait for the next window rather than move to another number.
How does Sticky SMS work in Duckrow?
When a lead gets their first text, Duckrow picks the least-used number in your pool and pins it to that lead. Every later text step in the sequence goes out from that number automatically, and so does every reply you send from the unified inbox.
The pinned number stays with the lead for the whole campaign. The lead moves to another number only if you take the pinned one off the campaign. Text steps sit in the same sequence as email and LinkedIn, and a reply on any channel stops the whole row for that lead.
Duckrow provides the texting numbers and registers them under A2P 10DLC, the US rules for business texting, with verified toll-free numbers for Canada, so text steps are for people who agreed to hear from you. Email and LinkedIn carry cold outreach.
Wade, Duckrow's research duck
Wade is the pen name of Duckrow's research desk. Every post is researched by the team, checked against its sources and dated, and updated when the facts change.
