An email sequence is an automated series of emails sent to a contact at set intervals, usually three to six steps over two to three weeks, that stops when the person replies, books, or unsubscribes. Tools such as Lemlist, Instantly, Smartlead and the sequencers inside Apollo and HubSpot run them. Every address in a sequence receives every step until it stops, so an invalid address does not bounce once but once per step, which is why sequences are the place where an unverified list does the most damage.
Sequences are measured by reply rate per step, positive reply rate, meetings, and the guardrails: bounce rate and spam complaint rate per sending domain. Most positive replies arrive on steps two and three; step one is rarely the best performer.
Sequencers suppress a hard-bounced address after the first bounce, but the bounce has already counted. Verifying the list before it enters the sequence is the only way to keep the first step clean. The B2B email tools roundup compares the platforms with list hygiene as the thread.
A four-step sequence loads 2,000 contacts. Unverified, 290 bounce on step one and the domain is throttled before step two. Verified first, 1,720 confirmed-valid contacts run all four steps, 9 bounce in total, reply rate is 7% and the domain is untouched for the next campaign.
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Verify Leads - FreeAyoub built BounceZero's 5-stage validation pipeline, its dedicated BGP-announced IP infrastructure, and the Patroni HA PostgreSQL cluster behind every verification. Previously built high-volume email delivery infrastructure. Trained at 1337 Benguerir (École 42 network, 2019). Open-source: bgp_analyzer.