SimpleVerifier Team · Reviewed
How do I clean an email list before sending?
Remove duplicates and malformed addresses, drop anyone who has bounced or unsubscribed, then run the rest through a verifier that does a real SMTP mailbox check. Send to the valid addresses, hold back or test the risky ones in a small batch, and never mail the invalid ones. Clean the list immediately before each campaign.
The order that works
Do the free steps first so you do not pay to verify rows you were going to delete anyway.
- Normalise: trim spaces, lower-case, and remove exact duplicates (and Gmail dot and plus variants if you want one row per person).
- Remove suppressions: previous hard bounces, unsubscribes and spam complaints never go back on a list.
- Verify: upload the CSV to a verifier that connects to the recipient's mail server and asks whether the mailbox exists. Syntax-only checkers cannot do this.
- Segment by result: valid goes in the campaign, invalid is suppressed, risky is handled separately (see the risky answer).
- Send in a small first batch and watch the bounce rate before sending the rest.
What cleaning cannot do
A verifier tells you whether an address is likely to accept mail. It cannot tell you whether the person wants it, whether you have consent, or whether your message will land in the inbox rather than spam. A clean list with a poor sending reputation still goes to spam; see what verification does and does not fix.
Related questions
- Is it safe to upload my list to a verifier?
- Check the vendor's privacy terms first. SimpleVerifier's privacy policy rules out using customer lists for our research, and the [security page](/security) describes how data is handled.
- Should I clean the list before or after importing it into my sending tool?
- Before. Importing first means bad addresses can be sent to by an automation before you get to them.
Sources
- Google email sender guidelines
- Bounce limits by platform, read from each vendor's own docs (SimpleVerifier, 1 Oct 2026)
Figures marked as ours come from SimpleVerifier’s own dated tests on made-up addresses, published with their data on the research page. No customer data is used, and we publish no accuracy percentage because we have no independent measurement to back one.
Do it now
Test it on a real address first
Type any address. It gets the same check the paid plans run: syntax, the domain’s mail servers and, where the provider allows it, a live mailbox check. Nothing is sent to the address.
Five checks a minute, no account needed. Nothing is sent to the address — we ask its mail server whether the mailbox exists, then disconnect.
Have a list? Sign in with Google and the first 100 addresses are checked free, with results to download. No card.
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