What is transactional email?

Open rates run far above marketing mail, often above 40%, because the recipient is waiting for it. That attention is the asset, and it is the reason the temptation exists.

Send it from a separate subdomain with its own authentication. A marketing campaign that damages reputation then cannot stop password resets from arriving.

Verification belongs at the point of capture for this traffic. A mistyped address at signup means the receipt never arrives, and the customer contacts support instead of reading it.

Latency matters here in a way it does not for marketing. A password reset that arrives four minutes late has already failed, because the user requested another one.

Say your store takes 8,000 orders a month and guests type their email at checkout on a phone. Suppose 1.2% of them mistype it. That's 96 orders a month where the confirmation goes to a dead address or, worse, to a stranger.

Follow one of them through your systems. The customer pays, sees the thank-you page, and waits for an email that never comes. By evening they've written to support asking whether the order went through. Some will dispute the charge with their bank instead. Your support team answers 96 avoidable tickets a month, and each one began with a swapped letter.

A check on the email field catches most of these while the person is still looking at the form. gmial.com gets a suggestion, and a domain with no mail server gets a prompt to look again. The order still goes through either way, because a checkout should never be blocked by a verification result.

Marketing bounce rules don't transfer well. When a marketing address hard bounces, you suppress it and move on. If a customer's account email hard bounces, suppressing it silently means they'll never get another receipt or reset link, and they won't know why.

So the bounce should change something in your product. Flag the account, and at the next login show a banner asking the person to confirm or update their email. For an order from a guest, show the support team a note on the order itself.

Soft bounces on this stream deserve patient retries. A full mailbox or a greylisting delay clears up, and the customer still wants the message when it does.

Measure this stream separately too. Track time from trigger to delivery, and alert on it. Many sending platforms let you create separate streams for transactional and broadcast mail, each with its own reputation and its own reporting. Use that split even if you're on a single domain today.