Moving email providers is more than changing an API hostname. Your application may depend on a template format, custom headers, scheduling behaviour, inbound processing or SMTP configuration. A migration succeeds when the entire workflow remains understandable before and after the switch.
Inventory what the application uses
List every message type and how it is triggered. Record sender domains, recipients, templates, attachments, scheduling and delivery callbacks. Identify capabilities that cannot be mapped directly to Sendar's current public API.
Our migration hub covers major transactional providers, including Resend, SendGrid, Postmark, Amazon SES, Mailgun and Brevo. Use the provider-specific guide as a mapping aid, then validate it against the exact workflow in your application. A guide is not proof that every feature of another platform has an equivalent.
Prepare without switching traffic
Verify the new sending domain and map one request into Sendar's format. Inspect the payload locally, then use an authorised address for a controlled test. Preserve your existing suppression and unsubscribe decisions rather than treating the new provider as permission to contact everyone again.
Keep application event identities stable through the migration. Otherwise, an event that was already handled by the old integration may appear new to the replacement.
Assign one sender to each event
Use a feature flag or routing rule to select the provider for the pilot workflow. Do not let both integrations send the same production message as an informal comparison. If you need a shadow check, compare payloads without submitting the second message.
Record which provider handled each event and its message ID. This makes delivery investigations and rollback decisions possible without guessing from the time of the deployment.
Define rollback before cutover
Write down the conditions that would stop the pilot, such as sustained request failures or a missing required field. Reverting the routing rule should affect new events without replaying old ones. Retain both sets of logs while reconciling pending work. Expand to the next workflow only after you can explain the pilot's results and support cases.