How to send email campaigns without landing in spam: a deliverability guide

When your messages land in spam, open rates fall, sales drop and the trust of your audience suffers. Mail providers use ever smarter filters, so simply pressing "send" on a list is a sure way to end up blocked. Deliverability, the share of emails that reach the inbox, is something you build with technical preparation, a clean list and good content.

Why a message ends up in spam

• The sender is not authenticated (missing SPF, DKIM or DMARC).
• The sending domain or address is new and has no reputation.
• Many recipients mark the email as spam, or never open it.
• The list contains old, wrong or purchased addresses that bounce.
• The message looks like spam: aggressive words, big images with little text, broken links.
• The sending speed suddenly jumps.

Step 1. Prepare your domain

• SPF: a list of servers allowed to send for your domain.
• DKIM: a digital signature that proves the message is genuine and unchanged.
• DMARC: the policy that says what to do if the checks fail, plus reports.
• Also make sure your sending server has a proper reverse DNS (PTR) and that you use your own domain in the "From" address, not a free mail service.

Step 2. Register with the mailbox providers' tools

Large providers offer free dashboards (for example Google Postmaster Tools) that show your domain reputation and spam rate. Sign up and look at them regularly. Where possible, also sign up for feedback loops, which tell you when someone marks your email as spam so you can remove them.

Step 3. Warm up a new domain or address

A new sender is treated with suspicion. Start small, with your most engaged contacts, and raise the volume gradually over two to four weeks. For example 50, 100, 250, 500 messages a day, and so on. Sudden big volumes from a new domain look like spam.

Step 4. Keep a clean list

• Collect addresses only from people who agreed (a double opt-in is safest and also GDPR-friendly).
• Never buy lists.
• Remove addresses that bounce and people who never open for six months, or try a last "do you still want this?" message first.
• Put a visible unsubscribe link and honour it at once. An easy unsubscribe is better than a spam complaint.

Step 5. Send a test first

Send the message to your own addresses at several providers and check where it lands. Look at it on a phone and a computer. Make sure all links work.

Step 6. Check the message with a tester

Free tools such as mail-tester.com give your email a score and show what to fix: authentication, content, blacklists.

Step 7. Write and design so it does not look like spam

• Use a clear, honest subject line and a real sender name.
• Avoid shouting: all capitals, many exclamation marks and words like "free money", "guarantee", "urgent".
• Keep a good balance of text and images. A message that is just one large picture is suspicious. Always add real text and alt text.
• Use simple, clean HTML and a plain-text version too.
• Use few links, and links to your own domain. Do not use link shorteners.
• Personalise with the name and relevant content. People open what is relevant to them.

Watch the numbers

• Bounce rate: keep it under 2%.
• Spam complaints: keep them under 0.1%.
• Open and click rates: a falling trend warns you before the problem is big.

Trust builds slowly and breaks fast. A small, interested, clean list that gets relevant emails will always beat a big list that is ignored.