Hi everyone, I'm new to marketing tools but I handle our infra. We just moved our email list from GetResponse to ConvertKit. Our infrastructure is the same — same sending domain, same DNS records (SPF, DKIM), same server IPs.
But our open rates fell by about 15% across the board. The content and send times are consistent. From an infrastructure or deliverability standpoint, what could cause this with the switch? Does ConvertKit handle IP reputation or throttling differently?
CloudNewbie
I'm a principal architect at a mid-market SaaS company with about 400,000 users, where I oversee the platform that includes our marketing automation stack. We've run both GetResponse and ConvertKit in production at different times, handling sends for several hundred thousand subscribers, and I've had to debug these exact deliverability cliffs.
From an infrastructure perspective, open rate drops almost always trace to sender reputation signals you can't see directly. The platforms differ in foundational architecture, which impacts how inbox providers treat your traffic. Your DNS records are just the entry ticket; the ESP's internal practices decide if you get a good seat.
1. **IP Pool Strategy & Warm-up:** GetResponse uses more dedicated IP assignment, especially at higher tiers, allowing reputation to be built per sender. ConvertKit heavily employs shared IP pools for efficiency. Your mail is now sharing an IP with potentially thousands of other ConvertKit senders. If just a few senders on that pool engage in poor list hygiene or spammy content, the entire pool's reputation suffers, impacting your deliverability. A 15% drop is a classic symptom of landing on a colder or noisier IP pool post-migration.
2. **Outbound Throttling & Connection Management:** These platforms use different MTA (Mail Transfer Agent) configurations and throughput limits. ConvertKit may be using a more aggressive concurrent connection limit per IP to manage costs, which can appear as throttling to receiving servers like Gmail or Microsoft. If their MTA opens and closes connections too rapidly, or if their outbound volume from a single IP spikes, it can trigger temporary filtering or routing to the "Promotions" tab, which crushes open rates.
3. **Engagement Tracking & Pixel Hosting:** The technical method of tracking opens differs. The open rate pixel is a tiny, hosted image. If ConvertKit hosts this image on a different subdomain or CDN with a poorer reputation score (like a generic cloud storage URL), some email clients or corporate firewalls may block it by default, falsely registering as an unopened email. Check the `src` attribute of the tracking pixel in the raw email source between the two platforms.
4. **Default Header Injection & Authentication:** Beyond SPF/DKIM, mailbox providers look at other headers like `List-Unsubscribe` and `Feedback-ID`. Each ESP implements these differently. ConvertKit's default header structure might be missing a key alignment or using a slightly different syntax that certain filters (like O365's) deprioritize. You need to validate the full, raw headers of a sent email from both systems, not just your DNS.
Given you're handling infra, I'd recommend ConvertKit only if your primary constraint is simplicity and cost for a small, highly engaged list under 10,000 subscribers. For any serious volume where deliverability is a business metric, GetResponse's architecture provides more isolation and control. To make a clean call, tell us your exact list size and the percentage of your list that's inactive (no open in >90 days).
Boring is beautiful