How to write emails that don't end up in spam

Forwarding only gets you halfway there. If the messages you send look like spam, they’ll be treated like spam — by Gmail, by Outlook, by Apple Mail. The fix is mostly habits, not infrastructure.

Write subject lines that match the email

• Keep them under 50 characters so they don’t get cut off on mobile.
• Use specific keywords. “Check this out” beats nothing, but “Q3 invoice for Acme” beats both.
• Don’t mislead. Clickbait subjects tank open rates over time and train recipients to ignore you.
• Personalize when it’s natural — recipient’s name, their company. Don’t fake it.

Make the call to action obvious

One primary action per email. State it clearly (“Confirm your address”, “View invoice”). Put it in a button or a clearly-labeled link, and repeat it once near the bottom of longer messages.

Avoid spam trigger words

“Free”, “guarantee”, “earn money”, “act now”, “100% off” — combinations of these trip filters even on legitimate mail. Test what you have with mail-tester.com before sending at scale.

Personalize and sign

Address recipients by name when you have it, and always include a signature with a real name and contact details. Generic mass-mail with no signature reads as spam to filters and to humans.

Limit images and links

A wall of images with two lines of text is a common spam pattern. So is twenty links in one message. Keep the image-to-text ratio sane and the link count low.

Test before you send

Before any campaign:

1. Open mail-tester.com and grab the test address.
2. Send your draft to it from the same client and address you’ll use in production.
3. Refresh mail-tester for a score and a list of issues — broken DKIM, suspicious words, missing list-unsubscribe.
4. Fix and repeat until you’re at 9/10 or better.

Other tools that do the same job: GlockApps, Litmus, Email on Acid.

Use double opt-in

For anything resembling a list: confirm email addresses with a click before sending. It cuts bounces, weeds out typos and bots, and is required by GDPR, CAN-SPAM, and CASL for most business contexts.

Stay consistent and use a real ESP

Recipients and filters build a sender reputation over time. Send irregularly, or from a brand-new domain, and you start at zero. A reputable ESP — Postmark, Mailgun, Resend, or similar — handles SPF, DKIM, DMARC, IP reputation, and list management for you. Don’t try to hand-roll bulk sending from a generic SMTP relay.

For one-to-one mail from your own domain, EForw’s catch-all forwarding plus Gmail send-as is enough. For lists, use a real ESP — that’s the line.