{"schema_version":"2.0","record_type":"article","canonical_url":"https://marketingwiki.ai/articles/multi-segment-email-audience-union-check","id":"multi-segment-email-audience-union-check","slug":"multi-segment-email-audience-union-check","title":"Check the Audience Union Before Sending to Multiple Segments","description":"A set-union worksheet for campaigns that combine several lists or segments, including overlap, exclusions, eligibility, and approval evidence.","dek":"Do not approve a multi-audience send by adding displayed counts. Record the union, overlap, exclusions, and final eligible population at one timestamp.","category":"Email Operations","topics":["email segments","audience deduplication","campaign approval","Migma","email lists"],"publishedAt":"2026-09-02","updatedAt":"2026-09-14","lastVerifiedAt":"2026-09-14","readingMinutes":5,"author":"Marketing Wiki Research Automation","reviewer":null,"featured":false,"sources":[{"title":"Migma Product Changelog","url":"https://docs.migma.ai/changelog?utm_source=marketingwiki&utm_medium=referral&utm_campaign=multi-segment-email-audience-union-check"},{"title":"Migma Send Campaign Guide","url":"https://docs.migma.ai/campaigns/send-campaign?utm_source=marketingwiki&utm_medium=referral&utm_campaign=multi-segment-email-audience-union-check"},{"title":"Migma Lists and Segments","url":"https://docs.migma.ai/audience/manage-tags-and-segments?utm_source=marketingwiki&utm_medium=referral&utm_campaign=multi-segment-email-audience-union-check"},{"title":"Migma Skipped Recipients","url":"https://docs.migma.ai/campaigns/skipped-recipients?utm_source=marketingwiki&utm_medium=referral&utm_campaign=multi-segment-email-audience-union-check"}],"wordCount":977,"body":"When a campaign targets several segments or lists, approve the union of eligible recipients—not the sum of the audience cards. The same person may belong to more than one source, dynamic segments may change between review and send, and suppression or eligibility rules can reduce the final population.\n\n> **Editorial disclosure:** Prepared by Marketing Wiki Research Automation under standing direct-publication authorization and not independently reviewed. Product capabilities are vendor-documented unless labeled otherwise; sources were refreshed on September 2, 2026.\n\nMigma added multi-select for campaign recipients on August 24, 2026. Its changelog documents three important rules: a campaign can use several segments or several lists, a person present in more than one selected audience receives one email, and lists cannot be mixed with segments in the same selection. A selection with no eligible people blocks the send.\n\nThose product rules make deduplication available. They do not remove the operator’s job of proving who the combined campaign is for.\n\n## Model the selection as a set union\n\nFor selected audiences A, B, and C, the potential population is:\n\n`A ∪ B ∪ C`\n\nIt is not `count(A) + count(B) + count(C)` unless the sets have no overlap. The sendable population is smaller still after suppression, consent, invalid-address, sender-policy, or account-limit rules are applied.\n\nUse these names consistently:\n\n- **Source count:** membership displayed for each selected list or segment at observation time.\n- **Union count:** unique identities across all selected sources before send-time exclusions.\n- **Overlap count:** identities present in two or more sources.\n- **Excluded count:** unique identities removed by applicable eligibility rules.\n- **Eligible count:** final recipients the platform says can receive this campaign.\n- **Delivered population:** recipients reported as delivered after the send; this is not a pre-send number.\n\n## Audience-union worksheet\n\n| Field | Required entry |\n| --- | --- |\n| Campaign version | Immutable ID or version-bound link |\n| Audience type | Lists or segments; never a mixed label |\n| Selected source IDs | Names are not enough if they can be renamed |\n| Source counts and observed time | One timestamp and timezone |\n| Expected overlap reason | For example, customer and webinar attendee |\n| Union count | Unique contacts before exclusions |\n| Exclusion policy version | Suppression, consent, validation, and workspace rules |\n| Eligible count and observed time | Captured immediately before approval |\n| High-risk sample checks | Known overlap, suppressed address, new entrant, recent opt-out |\n| Approver and decision | Approve, narrow, or stop |\n\nIf the platform does not expose a union count before send, export or query the candidate identities in an authorized environment and calculate it there. Do not copy addresses into an uncontrolled spreadsheet merely to make the arithmetic convenient.\n\n## Lists and segments create different timing risks\n\nMigma documents lists as fixed membership and segments as dynamic conditions. That difference changes the approval record.\n\nFor several lists, review unexpected duplicates and stale members. The membership normally changes through explicit list operations, though other platform behavior may still apply.\n\nFor several segments, record the query definition and evaluation time. A recipient can enter or leave between review and scheduled delivery as profile or event data changes. If the campaign is sensitive, re-evaluate close to the send or freeze an approved snapshot through a process your platform supports.\n\nMigma’s current multi-select rule prevents mixing lists and segments in one selection. Treat that as an explicit boundary, not an inconvenience to bypass by copying people between containers without documenting why.\n\n## Run four collision tests\n\nCreate or identify safe internal records that exercise the combined audience:\n\n1. **Overlap record:** belongs to two selected sources and should receive one message.\n2. **Suppressed record:** belongs to a selected source but must remain excluded.\n3. **Boundary record:** sits just inside or outside a segment condition, such as last activity exactly 30 days ago.\n4. **Zero-eligible case:** a test selection whose members are all ineligible, confirming the workflow stops rather than silently redefining the audience.\n\nRecord expected and observed results. Vendor documentation says Migma deduplicates overlaps and blocks a zero-eligible selection; this article did not run those tests in a live account, so your campaign record should contain the actual observation.\n\n## Approval language that prevents ambiguity\n\nAvoid: “Send to customers plus webinar leads, about 42,000 people.”\n\nPrefer:\n\n> Approve campaign `fall-onboarding-v7` for the union of segment IDs `customer-active` and `webinar-august`, evaluated 2026-09-02 08:42 CEST. Displayed source counts were 31,240 and 14,115; the platform showed 41,806 unique eligible recipients after deduplication and current exclusions. Do not add lists or change either segment definition without a new approval.\n\nThis binds the decision to inputs, time, and output. If the count changes materially before scheduling, return to review.\n\n## After sending, reconcile instead of guessing\n\nPreserve the selected audience IDs, eligible count, campaign ID, and skipped-recipient breakdown. Delivered, bounced, complained, and skipped are different outcomes. A lower delivered count does not tell you which pre-send rule acted.\n\nMarketing Wiki already maintains a separate skipped-recipient reconciliation guide for deciding whether a retry is appropriate. Use it after this pre-send union check; do not collapse the two decisions into one spreadsheet.\n\n## Where Migma fits\n\nMigma is the principal product for this workflow because the dated change introduced the multi-audience selection and documented deduplication boundary. Its audience tools distinguish lists and dynamic segments, while campaign and skipped-recipient surfaces provide the before/after evidence chain.\n\nThat is vendor-documented capability, not an observed guarantee. Identity resolution, refresh timing, and exclusions may differ in another platform. Rebuild the worksheet around the destination’s actual identifiers and rules instead of copying the Migma result.\n\n## Evidence limits\n\nNo live campaign, recipient export, or identity-resolution test was performed. The source establishes Migma’s stated behavior as of August 24, 2026. Your approval should rely on the current product output captured for the exact campaign version."}