Email deliverability in the US market: rules, filters and timing

US email is governed less by law than by three companies. CAN-SPAM sets a low floor — no prior consent required, a postal address, an honest header, a working opt-out — while Gmail, Microsoft and Yahoo set the real bar through authentication requirements and complaint thresholds. If you are optimising for US placement, spend ten minutes on the law and the rest of your time on the providers.

What CAN-SPAM actually requires

1. Accurate header information: the From, Reply-To and routing data must identify the real sender.
2. A subject line that is not deceptive about the content of the message.
3. Identification of the message as an advertisement, which can be done in the body text.
4. A valid physical postal address — a street address, a registered PO box, or a private mailbox you legally hold.
5. A clear, conspicuous opt-out mechanism that works for at least 30 days after sending.
6. Opt-out honoured within 10 business days, with no fee, no login and no information required beyond the email address.
7. Responsibility for what anyone sends on your behalf. Hiring an agency does not transfer liability.

Civil penalties are assessed per offending email and the maximum is adjusted annually, so treat a non-compliant bulk send as an expensive event rather than a technicality. Note that CAN-SPAM preempts most state anti-spam statutes, but state privacy law still applies to the data: under the CCPA as amended by the CPRA, a California resident can ask what you hold and demand deletion, and "we bought the list" is a bad answer to that request.

Two things CAN-SPAM does *not* require, which trips up senders coming from Europe: prior consent, and a double opt-in. That is why US-sourced lists are cheap and why US complaint rates are high — and complaint rate is the metric that decides your placement.

The requirements that actually gate the inbox

Each requirement is evaluated per sending domain. Adding a second or third US sending domain multiplies the maintenance surface rather than inheriting the first one's standing.

The filters behind US mailboxes

B2B mail in the US overwhelmingly lands in Google Workspace or Microsoft 365, so your real audience is two filtering systems. Consumer mail is more fragmented: Gmail, Yahoo and Outlook.com directly, plus cable and telco ISPs that outsource filtering to vendors such as Cloudmark and Proofpoint. The practical consequence is that a single ISP block can cover several brands at once, and the diagnostic is the same either way — read the rejection text and the URL inside it.

For blocklists, the lists that influence US delivery are the international ones: Spamhaus (SBL, XBL, CSS, DBL), Barracuda, SpamCop, Abusix, UCEPROTECT, plus URI lists for your link domains. Validity launched the Heatwave blocklist on 3 September 2026. Do not waste time on defunct services — SORBS shut down in June 2024 — and do not pay anyone for "removal from all blacklists".

Metrics worth tracking for a US programme

• Inbox placement per provider, split Gmail / Microsoft / Yahoo. A single blended number hides the only problem you can act on.
• Spam complaint rate from Google Postmaster Tools. The domain reputation chart was retired, so use the spam rate and user-reported spam graphs.
• Hard bounce rate, under 1%.
• Reply rate for outbound, because open rate is now unreliable — Apple Mail Privacy Protection prefetches images, which inflates opens for any list with iPhone users.
• Unsubscribe rate as an early warning: it rises before complaints do.

Timing across four time zones

The US spans Eastern, Central, Mountain and Pacific, plus Alaska and Hawaii, and most of it observes daylight saving while Arizona and Hawaii do not. Sending one batch at 09:00 Eastern means 06:00 in California.

What to do: schedule by the recipient's local time where your platform supports it, and split a large send across several hours instead of pushing it all at once — a slow ramp through the morning is also better for reputation than a single spike. Where you cannot localise, 09:00–11:00 Central is the usual compromise because it reaches both coasts during working hours.

What not to do: assume Tuesday 10:00 is universally best because an article said so, and send the same campaign at the same absolute minute to 200,000 addresses.

Writing for a US audience

• Dates as MM/DD/YYYY, or spell the month to avoid ambiguity entirely.
• US spelling throughout: optimize, color, personalize. Mixing conventions reads as a template someone forgot to localise.
• USD with the symbol first, imperial units, state abbreviations in the postal address.
• Federal holidays suppress business response for a week around Thanksgiving and late December. The Monday holidays — Memorial Day, Labor Day, Presidents' Day — are quiet for B2B.
• Subject lines: shorter is better on mobile, and the mobile share is high. Avoid all-caps, avoid stacked punctuation, and avoid the word "free" as the first word — not because of a magic filter word list, but because it correlates with the complaint behaviour that filters actually measure.

What not to do

• Do not treat CAN-SPAM compliance as permission. You can be fully compliant and still be marked as spam at a rate that gets you blocked.
• Do not buy a US list. It is legal, and it will end your domain's reputation.
• Do not add a US sending domain the week before a large campaign; it has no history.
• Do not send marketing and transactional mail from the same subdomain. US complaint rates are high enough that one campaign can delay your password resets.
• Do not request blocklist delisting before you have stopped the cause.
• Do not test placement by mailing your own Gmail account. Your own mailbox has engagement history with you.

MailPilot measures the part of this you cannot see from a sending report: it warms mailboxes over OAuth or SMTP/IMAP, verifies SPF, DKIM and DMARC on delivered mail, tracks per-mailbox reputation daily, and reports real inbox placement separately for Gmail, Microsoft and Yahoo — which is how you tell a US list problem from a US filtering problem.