One script per source ESP. Lists, contacts, list memberships, segments, templates, suppressions, scheduled campaigns — all transferred. The handful of things that don't auto-translate get flagged for manual review with a copy-paste-ready remediation.
Each guide has a tested, end-to-end migration script and a cutover checklist. Most customers complete the move in under a day.
For Twilio-account customers ready to leave the credits-pricing maze.
For ecommerce + B2B teams whose Klaviyo bill keeps growing faster than their list.
For teams that loved the quickstart but hit the wall on EU residency or marketing automations.
For the Mailgun veterans tired of the dashboard archaeology.
For Postmark shops that need marketing email in-product, not in a second tool.
For teams outgrowing Mailchimp's audience model and ready for predicate-based segments.
CSV-driven path. Bring your contact lists; we'll handle the rest.
Heavy automation users — we'll translate flow logic.
For teams that want to keep HubSpot CRM but offload the email send infrastructure.
Honest about the edges. Things in the right column need 5–30 minutes of manual remediation; we generate the TODO list automatically.
| Concept | Auto-migrates | Notes |
|---|---|---|
| Profiles / contacts (incl. custom fields) | Yes | Dedup on (account, email). Source IDs preserved as external_id. |
| Lists + list memberships | Yes | Opt-in setting (single vs double) preserved. Subscribed/unsubscribed status carried. |
| Suppressions (bounces, unsubs, complaints) | Yes | Imported into Relayly's suppression list before first send so you never re-mail a hard-bounced address. |
| Email templates (HTML) | Yes | Verbatim HTML transfer. We re-render in our drag-drop editor on demand. |
| Templates with placeholder syntax | Partial | SendGrid Handlebars / Postmark Mustache / Klaviyo Liquid → our Liquid. Most rules translate; we flag the rest. |
| Segment definitions | Partial | Predicate DSLs differ. We translate the common ~80% of predicates; you review the rest in <5 min per segment. |
| Drafts + scheduled campaigns | Yes | Audience and template references rewired to Relayly equivalents. |
| Sent campaign history (analytics) | Optional | Imported as read-only metadata, not re-delivered. Toggle off if you don't care about historical reporting. |
| Automations / Flows | Per-vendor | SendGrid Automations + Mailchimp Customer Journeys translate well. Klaviyo and ActiveCampaign flows need engineering review. |
| API keys + webhooks | Manual swap | Generate Relayly keys, find/replace in your codebase, update webhook URLs in your destination service. Most teams script this in 15 min. |
| Sender reputation / IP warmup | N/A | You can't move IP reputation between providers. Use our 14-day warmup curve in parallel — most teams see equivalent inbox rates by day 7. |
Same shape across every source ESP. Total wall-clock: usually under a day; only ~30 minutes is your team's time.
One Python script per source ESP. Reads from their REST API, writes a snapshot folder of CSVs + SQL.
The script outputs a manifest.json with what migrates cleanly, what needs review, and copy-paste remediation.
Idempotent SQL + CSV importers. Re-runnable safely until the diff is empty.
Send your next campaign through Relayly. Compare inbox rate at Gmail / O365 / Yahoo. If equal-or-better, cut over.
If you migrate to Relayly and the migration loses a subscriber, mismaps a segment, or causes a bounce on someone you previously sent to successfully — show us the diff and we'll fix it on us. Hands-on engineering time, not a support ticket.
This is enforceable on Pro tier and above. Free-tier customers get the same tooling but support is best-effort.
If you're moving from something we haven't documented yet — drop us a line. Most ESPs have a similar export shape; we'll write the import for you, often in under a week.
Email migration team All contact info