Definition
A suppression list is a do-not-send list. Every address on it is excluded from campaigns, even if it appears again in a new import.
What usually goes on it:
- Unsubscribes. People who asked to stop receiving your mail.
- Hard bounces. Addresses that permanently failed.
- Spam complaints. People who reported your email as spam.
- Verified-invalid addresses. Ones a verification tool marked as undeliverable.
- Manual requests. Do-not-contact requests that came by reply, phone or a privacy request.
Most email platforms and sequencers keep a suppression list automatically for bounces and unsubscribes. Problems start when data moves between tools.
Why it matters
Honouring opt-outs is required by law in most places. In the US, CAN-SPAM requires opt-out requests to be honoured within 10 business days. Gmail and Yahoo require bulk senders to process unsubscribes within two days. Under GDPR, a person's objection to direct marketing must be respected.
It also protects reputation. The most common way suppressed addresses get emailed again is a fresh import: a new lead export, a CRM sync, or a list moved to a new platform without its suppression history. The old bounces come back and bounce again.
Keep one master suppression list that every sending tool checks, and carry it with you when you switch platforms.
How SimpleCold handles it
SimpleCold does not manage your suppression list, but its results feed it. Undeliverable addresses with a failType of permanent are ones you can add straight away. When you upload a CSV to the bulk email verifier, the download keeps your original columns and adds Result, Reason code and Retry later, so filtering out suppress-worthy rows is a spreadsheet filter.