Deliverability is whether your email reaches the inbox. Authenticate your sending domain with SPF, DKIM and DMARC, add one-click unsubscribe, keep the spam complaint rate below 0.10%, send only to people who asked, remove inactive addresses, ramp up new domains slowly, and watch Google Postmaster Tools. Gmail and Outlook require this from senders of more than 5,000 messages a day, and Yahoo from bulk senders.
What decides deliverability
Mailbox providers decide where a message lands from four things:
- Authentication: DNS records that prove the mail comes from you.
- Reputation: how recipients treat your mail, from spam complaints to opens, replies and deletions.
- List quality: whether the addresses are real, current and asked for your mail.
- Content and sending pattern: honest subject lines, consistent volume, working links.
Authentication: SPF, DKIM and DMARC
SPF lists the servers allowed to send for your domain; DKIM signs each message so it can be checked; DMARC tells receivers what to do when a message fails those checks and where to send reports. DMARC.org's overview describes three policies: none (reports only), quarantine (treat as suspicious, usually the spam folder) and reject (refuse the mail).
Google's sender guidelines require every sender to use SPF or DKIM, and senders of more than 5,000 messages a day to Gmail accounts to use SPF, DKIM and DMARC; the DMARC policy can be none. DKIM keys must be at least 1024 bits, and Google recommends 2048.
The Gmail, Yahoo and Outlook rules
The three largest consumer mailbox providers now publish their requirements:
- Gmail (from 1 February 2024, more than 5,000 messages a day): SPF, DKIM and DMARC; one-click unsubscribe for marketing messages plus a visible link in the body; spam rate below 0.10%, never 0.30% or higher.
- Yahoo (sender best practices, enforced from February 2024): SPF and DKIM, and a DMARC policy of at least none that passes; a working one-click unsubscribe, processed within 2 days; spam rate below 0.3%.
- Outlook (Microsoft, April 2025): domains sending more than 5,000 emails a day to Outlook.com, Hotmail and Live addresses need SPF, DKIM and DMARC of at least none with alignment; from 5 May 2025 failing mail goes to Junk, with rejection to follow.
Spam complaints and unsubscribes
The spam rate is the share of your messages that recipients mark as spam. Gmail asks bulk senders to stay below 0.10%. The surest way to keep it low is to make leaving easy: a one-click unsubscribe in the header, as Gmail and Yahoo require, and a plain unsubscribe link in the body. Someone who cannot find the link presses the spam button instead.
List hygiene
A clean list protects reputation:
- Send only to people who asked, and keep a record of when and how they did.
- Use confirmed sign-up where lists attract fake or mistyped addresses.
- Remove hard bounces at once.
- Run a win-back to addresses inactive for several months, then remove those who do not respond.
- Never buy or rent lists.
Warming up a new domain or platform
A new sending domain, IP address or email platform has no reputation yet. Start by sending to your most engaged recipients, raise volume over a few weeks, and watch complaints and bounces before each step. Moving platforms counts: authenticate the new setup before the first send, and keep sending patterns steady during the move.
Monitoring
Google's Postmaster Tools show, for mail sent to Gmail, your compliance status against each requirement, your spam rate, IP and domain reputation, authentication results, encryption and delivery errors, usually updated within 24 hours. Pair it with your platform's bounce and complaint reports and with DMARC reports, and check them weekly. If you keep leads and customers in a CRM, sync unsubscribes and bounces both ways so nobody is emailed after leaving; our CRM implementation work covers that.
Deliverability checklist
Eight checks, in the order we run them:
- SPF record lists every service that sends for you.
- DKIM signing on, with a 2048-bit key where the platform allows.
- DMARC record published, starting at p=none with reports, moving toward quarantine or reject.
- One-click unsubscribe header and a visible link in every marketing email.
- Spam rate checked weekly in Postmaster Tools; below 0.10%.
- Hard bounces removed; inactive addresses re-engaged or removed.
- New domains and platforms warmed up over weeks.
- Unsubscribes synced to the CRM.
Conclusion
Email deliverability depends on authentication, reputation, list quality and the mailbox providers' rules. Gmail and Yahoo since February 2024, and Outlook since May 2025, require SPF, DKIM and DMARC from senders of more than 5,000 messages a day; Gmail and Yahoo also require one-click unsubscribe, and Gmail asks for a spam rate below 0.10%. Authenticate, make leaving easy, keep the list clean, warm up new setups and watch Postmaster Tools weekly.
PromotEdge International is an international strategy, technology, marketing and design company, and our delivery team is in India. Our email marketing team sets up authentication, list hygiene and monitoring as part of every program, in your own accounts.
Facts we rely on: see our company facts for what we state about ourselves and where each fact comes from.