Check authentication first
Send a test message to a Gmail account, open the message menu and choose the option to show the original. It lists SPF, DKIM and DMARC results. Fails or missing results are the first thing to fix. Authentication is also the most common reason that mail from a website contact form lands in spam, because forms often send from the web server rather than your mail provider.
Send from the right place
If your site sends notifications through its own server, consider connecting it to a proper mail service so messages go out through authenticated channels. Using a free webmail address as the From address for a service that sends on your behalf can also cause failures, since the webmail provider did not authorize it.
Keep the From name and address consistent. Constant changes look suspicious.
Understand sender reputation
Mailbox providers track how recipients treat mail from your domain and sending address. Many complaints, bounces to invalid addresses, and low engagement damage reputation. A new domain with no history may also be treated cautiously until it builds a record.
Warm up a new sending setup by starting with small volumes to people who expect to hear from you.
Clean up content and formatting
Messages made entirely of one large image, shortened links from public link services, all-capital subject lines, heavy promotional wording and attachments from unknown senders raise suspicion. Include real text, a clear signature with your business name and a physical or contact detail, and a plain-language subject.
For marketing mail, include an easy unsubscribe option and honor requests quickly.
Keep your list healthy
Only email people who have a relationship with you. Remove addresses that bounce. Do not buy lists. If a recipient says your mail went to spam, ask them to mark it as not spam and add you to their contacts, which helps their provider learn.
If you are still stuck, check whether your domain or sending IP appears on a blocklist using a public lookup tool, and review messages from your email provider. When the cause is not obvious, a web or IT professional can trace it through mail headers.
A practical test routine
Create a few free test mailboxes with different providers and send the same message to each. Note where it lands. Try a plain text version and a formatted one, with and without links. If only formatted mail fails, content is the likely cause. If everything fails, look at authentication and reputation.
Record the date, the result and any change you made. Changing three things at once leaves you unsure which one helped. Make one change, wait for DNS to settle, and repeat the test.
Also consider the human side. A message that opens with a generic greeting, hides the sender's name, or pushes an urgent payment link looks like phishing even when it is genuine. Plain, personal wording from a recognizable name helps both filters and readers.
Common questions
Why do only some people receive my mail in spam?
Each provider uses its own filters and the recipient's history with you. Gmail, Outlook and others can treat the same message differently.
Will asking customers to whitelist me help?
It can help for that person, but fix authentication so it works for everyone.
Does a new domain hurt deliverability?
A brand-new domain has no reputation yet, so start with low volume and steady, wanted messages.
This guide is general information. Search engines change how they work and their guidelines; check Google's current documentation for your situation. Nobody can guarantee a ranking.