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Learn how email sending works

Short essays on why mail providers treat senders the way they do, and what that means for you. Each one links the provider's own page.

  • Why a new mailbox starts slowly

    A mailbox that has never sent mail has no history with the providers that receive it. Here is what that means for your first weeks, and what warmup can and can't do about it.

  • SPF, DKIM and DMARC, one record at a time

    Three records in your domain's DNS tell the world that your email really comes from you. Here is what each one does, in what order to set them up, and how to tighten DMARC without losing real mail.

  • What Gmail, Yahoo and Outlook ask of senders

    Gmail, Yahoo and Outlook.com each publish rules for mail sent to their users. Here is what each one asks, what happens when you miss a rule, and which parts colding does for you.

  • Letting an AI agent send email without losing control

    An AI agent can read your inbox, write replies and send them. Here is what to give it, what to keep for a person, and how to stop it when it gets something wrong.