Deliverability, without the folklore

Deliverability advice online is about eighty percent folklore. Avoid the word “free”. Never use more than three links. Do not attach images. Keep your text-to-image ratio at 60:40, a number someone invented in 2011 and nobody has questioned since.

None of that is how modern filtering works. Here is what actually decides whether your issue lands, roughly in order of weight.

1. Authentication

If SPF, DKIM and DMARC are not set up correctly on your sending domain, nothing else you do matters. Gmail and Yahoo both require authentication for bulk senders now, and “bulk” starts at 5,000 messages a day — which sounds like a lot until you have two thousand subscribers and send twice a week.

Your provider will have a page on this. Do it properly, with your own domain, not their shared one. Then verify it independently: send yourself an issue, open the raw headers, and check for three pass results. Do not trust the dashboard’s green tick.

2. Engagement, and specifically recent engagement

Mailbox providers watch what your recipients do. Opens are a weak signal now that image proxying is standard, but these are strong:

• Replies. Enormously strong. One reply is worth a hundred opens.
• Moving a message out of spam.
• Adding you to contacts.
• Clicking through and staying.

And the negative ones: deleting without opening, repeatedly, over weeks. That is the signal that quietly kills a list.

3. List hygiene

This is where most small senders are losing, and it is the easiest to fix. If a third of your list has not opened anything in a year, every send is telling Gmail that two thirds of the people who receive your mail do not want it.

Suppress anyone with no engagement in twelve months. Not delete — suppress, so you keep the record. Send them one re-permission email first if it makes you feel better, but do not send six.

A smaller list that gets opened is worth more than a big one that gets ignored, and this is not a metaphor. It is literally how the scoring works.

4. Consistency

Sending 400 messages a week for six months and then 9,000 in one afternoon looks like exactly what a compromised account looks like. If you are about to send to a much larger list than usual — after a big signup spike, say — ramp it. A few thousand at a time, over a few days.

What barely matters

• Specific words. Filters have been statistical for fifteen years; no single word triggers anything.
• Number of links, unless they point to domains with bad reputations of their own.
• Emoji in subject lines. Annoying, not filtered.
• Image-to-text ratio. A pure-image email is a problem because it is unreadable, not because of a ratio.

The one test worth running

Before a send, mail the issue to accounts on Gmail, Outlook and one corporate domain if you have access to one. Not to check if it arrives — to check where. Gmail’s Promotions tab is not spam, but it is not the inbox either, and for a lot of newsletters that tab is where the open rate went.

If you are landing in Promotions and want out: fewer tracking parameters on your links, fewer images at the top, and more replies. That last one is the real lever, which is why every good newsletter ends with a question.

Next issue: how to end one.