Migrate from Customer Database App to Mailchimp

Scoped extraction and schema inference

We request a full CSV export from Customer Database App, covering all contacts and their associated fields, groups, tags, birthday dates, and pipeline stage labels. Because the app has no API, extraction is a customer-initiated export step that we guide through. We infer the active field schema from the column headers of the first export file and produce a written field inventory that maps each inferred field to a Mailchimp merge field type (text, number, date, address, phone). We also confirm whether MySQL sync is in use and, if reachable, extract from the MySQL copy for completeness. We flag the total contact count against the customer's target Mailchimp tier during this phase.

Mailchimp audience and merge field setup

We create or identify the target Mailchimp Audience and configure all required merge fields before any data import. This includes FNAME, LNAME, PHONE, and any custom fields mapped from the source schema. Date fields (including birthday) are created as DATE-type merge fields. Multi-value group and tag data are not pre-created as merge fields but will be applied as tags during the import phase. We set the correct merge field types at this stage to avoid import rejections later.

Data transform and tag normalization

We transform the extracted CSV into Mailchimp-compatible JSON records, applying the field mapping established in scoping. Group and tag label strings are split into individual tag entries. Pipeline stage values are prefixed with pipeline_ and applied as tags. Birthday dates are converted to YYYY-MM-DD format. Free-text fields containing commas are escaped. Any contact missing a valid email address is written to a separate rejection CSV with the reason listed for the customer's review. Contacts without emails cannot be imported into Mailchimp and are not migrated.

Batched import via Mailchimp Marketing API

We import records into Mailchimp using the Marketing API's batch upsert endpoint, chunking at 1,000 records per batch and adhering to Mailchimp's rate limit of 200 requests per minute with exponential backoff on 429 responses. Tags are applied as part of the member record payload. Each batch is validated for success before the next begins. We track the total accepted count, error count, and per-record error messages returned by the API. Any record rejected by Mailchimp (invalid email format, duplicate on a list with unique-email enforcement, merge field type mismatch) is written to the rejection report.

Reconciliation and supplemental export delivery

We compare the total records in the source CSV against the total accepted records in Mailchimp and investigate any gap exceeding 1 percent. We deliver the rejection CSV with failure reasons to the customer's admin for correction and re-import. We deliver a separate pipeline-stages CSV listing every contact's pipeline stage name for manual re-entry. We deliver the vouchers supplemental CSV for manual re-entry in a loyalty management tool. We deliver a written automation and workflow rebuild inventory — covering any implied automations the customer may want in Mailchimp (welcome series, birthday emails, re-engagement campaigns) — as a reference for their marketing team to rebuild post-migration.

Cutover and post-migration sign-off

We confirm the final record count in Mailchimp matches the expected migration total within the acceptable reconciliation threshold. We verify tag distribution, birthday merge field population, and address field completeness on a random sample of 20-30 records. We hand off the automation rebuild inventory and the pipeline and voucher supplemental exports. We do not manage Mailchimp automations as part of standard migration scope; that is a separate marketing implementation engagement.