Braze Checks Email Syntax, Not Mailboxes: Verify Before You Import

Braze accepts any address that's well formed. Its validator checks the shape of the address and stops there: no MX lookup, no mailbox check. Everything else is learned from bounces, which on a fresh Braze setup means your new sending domain and IPs take the hit. Verify the file before import and most of those bounces never happen.

Sources, read 2 November 2026: Braze's docs on email validation, importing your email list, CSV import and the email FAQ.

What Braze checks and what it doesn't

Check	Braze
Local part (before @)	1 to 64 characters, no whitespace or double quotes, no leading or trailing period; Gmail local parts at least two characters; stricter period rules for Microsoft domains
Domain (after @)	At least two labels, no IP addresses, Unicode must be Punycode, TLD on ICANN's list
MX record	Not checked
Mailbox exists	Not checked
After a hard bounce	Address marked invalid, no further sends; subscription state unchanged

That's a syntax check, not verification. The difference is covered in email validation vs verification.

Step by step

1. Export from the old platform with statuses.
2. Set the suppression list aside. Braze's guide says not to import unsubscribes, complaints and hard bounces as users. Keep them as a block list.
3. Keep recent engagers. Braze recommends users who opened in the last six months. The inactive subscriber finder splits an export into active, cooling and sunset groups.
4. Run a syntax pass with the bulk email syntax checker so Braze doesn't drop values on import.
5. Verify the rest on the verify page and remove invalid results.
6. Dedupe. Braze warns that duplicate profiles sharing one address break multi-criteria campaigns and reporting; the duplicate contact finder catches them.
7. Import the CSV with one identifier column (external_id, email or others) and, if you use subscription groups, subscription_group_id plus subscription_state. Files of default or custom attributes can be up to 500 MB.

What verification can't settle

Catch-all domains accept every address at the server, so a single mailbox can't be confirmed; Microsoft consumer mailboxes (outlook.com, hotmail.com) often don't answer single-mailbox checks reliably. Those come back risky or unknown. Import them, but send them after the verified group so real bounces can settle them. And because a Braze hard bounce leaves the subscription state alone, keep your own hard bounce list if other tools read subscription status.

Where SimpleVerifier fits

Verify the file on the verify page; the first 100 checks are free with a Google sign-in. Pro is $39 a month with the first 100,000 checks a month at full speed, then slower, never cut off. For new sign-ups, real-time verification on signup forms checks mailboxes before profiles are created. See pricing.