Transactional email only works if it reaches the inbox
A password reset that lands in spam is a locked out user. A receipt that never arrives is a support ticket. Transactional email is infrastructure, and the difference between email that works and email that does not is almost entirely about authenticating your domain so that receiving servers trust you.
Authenticate the sending domain
Three DNS records decide whether your mail is trusted. SPF says which servers are allowed to send for your domain. DKIM signs each message so the receiver can verify it was not tampered with. DMARC tells receivers what to do when a message fails those checks. Set all three on the domain you send from, and your deliverability stops being a mystery.
SPF TXT v=spf1 include:the-provider ~all
DKIM TXT (the signing key the provider gives you)
DMARC TXT v=DMARC1; p=none; rua=mailto:dmarc@yourdomain
Until these verify, treat your sending as experimental. A real lesson from this stack: mail can sit unverified for days when the records are added to the wrong DNS zone, because the domain's nameservers point somewhere other than where you edited. Confirm the records resolve on the live nameservers, not just that you saved them.
Send from the right address
Send from a real subdomain or address on your own authenticated domain, not from a free mailbox. Set a reply to that a human actually reads. The from name and address are the first thing a recipient and a spam filter both judge, so make them consistent and recognizable.
Compose with code, keep it plain
Build the email as a component so the receipt the user gets matches the brand they just bought from, and keep the copy plain and human. Transactional mail is not the place for heavy imagery and marketing flourishes; those hurt deliverability and bury the one thing the user opened the message to find, the link, the code, or the confirmation.
Know where email sits in the channel mix
In a market where SMS and WhatsApp carry the important moments, email is the secondary rail: good for receipts, statements, and records, weaker for anything urgent. Send the time critical message over the channel the user actually checks, and use email for the durable paper trail. Matching the message to the channel is what makes the whole communications layer feel reliable rather than noisy.