What is transactional email?
Transactional emails: messages that always arrive on time
Transactional emails are the messages your system sends automatically after a single user's action: an order confirmation, a password reset, an invoice, a notification. Not marketing, then, but promises your system makes to your customer — and they have to land in the inbox within seconds. 2mail builds the infrastructure for that: a separate sending channel with authentication, retry logic and full logging.
What are transactional emails?
Transactional emails are messages your system sends automatically as the direct result of a single user's action: an order, a password reset, an invoice, a payment confirmation. The recipient triggered it themselves, expects the message — and expects it immediately.
That is what sets them apart from a newsletter or campaign, which you schedule yourself and send to an entire list in one go. Transactional emails — also called system emails — go out one at a time, the moment something happens, and their content differs per recipient. Nobody subscribes to them and nobody unsubscribes: they are part of the service itself.
That is why transactional mail is business-critical in a way marketing mail is not. A campaign that leaves an hour later is annoying; a password reset that keeps someone waiting for an hour is a support ticket — or a customer who gives up. If these emails are slow, land in spam or simply disappear, that directly undermines trust in your service.
Examples of transactional emails
Six types come back in almost every business. They have one thing in common: the recipient has just done something and is waiting for the message.
| Type | What triggers the message | Sample subject line |
|---|---|---|
| Order confirmation | A customer completes an order in your web shop. | Your order #10482 is confirmed |
| Shipping notification | The parcel is handed over to the carrier. | Your parcel is on its way — track it here |
| Password reset | A user clicks "forgot password". | Reset your password |
| Account verification | Someone creates an account or changes their email address. | Confirm your email address |
| Invoice or payment confirmation | A payment comes in or an invoice is created. | Invoice 2026-0412 for your subscription |
| System alert | A threshold is exceeded, a job fails or a login happens from a new device. | New sign-in to your account |
Four places where system mail is business-critical
From the first order to an alert at 3 a.m. — these are the emails your customers and colleagues genuinely expect.
Order confirmation
Right after the purchase, your customer wants it in black and white that the order went through. If that confirmation fails to arrive, doubt follows, along with a support email or a duplicate order. 2mail delivers the confirmation — and the shipping notification after it — within seconds.
Order #10482 confirmedPassword reset
A reset link that arrives too late is the most frustrating experience a user can have with your app — and an immediate reason to drop out. Account verifications and magic links require the same immediate, reliable delivery.
Your reset link is valid for 30 minutesInvoice & payment confirmation
Invoices and payment confirmations come straight out of your accounting or invoicing software and by definition contain customer data. They have to arrive, and you have to be able to demonstrate afterwards that they did — 2mail takes care of both with logging per send.
Payment received · invoice 2026-0417Alerts & notifications
A failed backup, a disk filling up, a monitoring alert: these are emails that have to reach the right person immediately, including outside office hours. A delay or a spam folder makes such an alert worthless.
Alert · backup failed on node-03The journey of a system email
From an event in your application to a traceable delivery confirmation — in four steps.
Event in your app
A customer places an order or requests a reset. Your application composes the email and hands it over to 2mail via SMTP.
2mail relay & authentication
The mail arrives on the transactional channel, is signed with SPF, DKIM and DMARC and queued for immediate sending.
Delivery with retry
The receiving server accepts the mail. If that temporarily fails — greylisting, throttling — 2mail retries automatically.
Logging & follow-up
The send, the delivery and any bounce are recorded. When a support question comes in, you find the answer straight away.
Transactional is not marketing
Mailbox providers assign reputation per IP and per domain, not per email. If you run both streams through the same infrastructure, your password reset shares the reputation of your latest newsletter.
Transactional
Via 2mail — the critical channel
- Triggered by a single user — the direct result of one concrete action.
- Sent individually & immediately to one existing, active address.
- Expected by the recipient, so a very low chance of spam complaints.
- Zero tolerance for delay — too late is as good as not arrived.
Marketing
Campaigns — the promotional channel
- Triggered by you — you decide when a campaign goes out.
- Sent in bulk to large lists in a single sending moment.
- More prone to complaints & bounces, which weighs on reputation.
- Tolerates postponement — leaving an hour later is not a problem.
Five common mistakes with transactional email
Most problems with system mail are not in the content of the message, but in the way it is sent.
Sending everything over one channel
If you send order confirmations and newsletters from the same sender and over the same infrastructure, the reputation of your campaigns weighs on your system mail too. One badly received campaign is enough to slow down password resets as well.
Sending without SPF, DKIM and DMARC
Without authentication, a receiving server cannot verify that the message really comes from your domain. Gmail, Yahoo and Microsoft refuse such mail or put it in the spam folder, however correct the content is.
Promotion in a transactional email
An order confirmation with a banner for the sales becomes a marketing message: consent and a way to unsubscribe then apply, and spam filters judge the message that way too. Keep transactional mail to the transaction.
Not following up on bounces and logs
A system email that does not arrive does not report itself. If you do not process bounces and keep no log per message, you only hear about it from the customer who never received their invoice or reset link.
Using the mail server of your web hosting
The PHP mail function or the shared mail server of a hosting plan shares its IP address with every other customer on that server, and usually has a limit per hour. That is enough for a contact form, not for mail a customer is waiting for.
Sending a transactional email via SMTP
For your application, a transactional email is an ordinary SMTP send: connect on port 587, encrypt the connection with STARTTLS, log in and hand over the message. Below is the complete example in Python. Login and password come from environment variables, not from the code; replace example.com with a domain you have authenticated in 2mail.
import os
import smtplib
import ssl
from email.message import EmailMessage
msg = EmailMessage()
msg["From"] = "Example <noreply@example.com>"
msg["To"] = "you@example.org"
msg["Subject"] = "SMTP test"
msg.set_content("Sent through the 2mail SMTP relay.")
context = ssl.create_default_context()
with smtplib.SMTP("relay.2mail.eu", 587, timeout=10) as server:
server.starttls(context=context) # upgrade to TLS first, log in afterwards
server.login(os.environ["SMTP_USERNAME"], os.environ["SMTP_PASSWORD"])
server.send_message(msg) # call again for the next message, same connectionIf a newsletter attracts spam complaints or high bounce rates, that can drag down the delivery of your invoices and resets — exactly the emails that cannot take any delay. At 2mail, transactional and marketing mail therefore run over separate sending streams, each with its own reputation build-up. Your transactional channel is authenticated with SPF, DKIM and DMARC per domain and runs on Belgian servers that meet the GDPR requirements for processing personal data.
Want to know how to connect an application technically? Read how the 2mail SMTP relay works, or dive into deliverability to understand why authentication and reputation determine whether your mail reaches the inbox.
And the other stream? That is described under email marketing and campaigns, with the practical side — list, authentication, spreading and measurement — under sending a mailing.
Frequently asked questions about transactional email
Need reliable system mail?
Connect your application to the 2mail SMTP relay and let your order confirmations, password resets and invoices arrive exactly when they should. JAAN bv has provided email infrastructure for Belgian companies from Zelzate since 2000, with personal support at every step.
