SMTP (Simple Mail Transfer Protocol) is the standard set of rules email servers use to send messages from one place to another. When you hit send, your email program hands the message to an SMTP server, which passes it along until it reaches the recipient's mail server.
That is the whole idea. Receiving and reading mail uses different protocols (IMAP or POP3). SMTP only handles the outgoing trip.
Why SMTP matters when you do outreach
When you send one email from Gmail, you never think about SMTP. Gmail handles it. When you start sending campaigns from an outreach tool, you have to tell that tool how to send on your behalf, and SMTP is usually the answer.
This matters for a few practical reasons:
- It controls which address your email comes from. Sending through your own mailbox's SMTP means replies land in your real inbox, and the recipient sees a normal sender.
- It ties your sending to your domain's reputation. Every message sent through your mail server reflects on your domain. Careless sending can hurt your regular business email too.
- Providers set limits. Each email host caps how many messages you can send per day or per hour. Go over and messages bounce or the account gets paused.
- Authentication happens around it. Records like SPF, DKIM and DMARC on your domain tell receiving servers that your SMTP server is allowed to send for you. Without them, more of your mail is likely to land in spam.
In short, SMTP is the pipe. If the pipe is set up badly, the best email copy in the world won't arrive where you want it.
What the settings actually look like
Any tool that sends through SMTP will ask for the same handful of details. Your email host lists them in its help pages.
| Setting | What it means | Typical value |
|---|---|---|
| Host | The address of your provider's outgoing server | smtp.yourprovider.com |
| Port | The channel used to connect | 587 (STARTTLS) or 465 (SSL) |
| Username | Usually your full email address | you@yourdomain.com |
| Password | Your mailbox password or an app password | Set by you |
| Encryption | How the connection is secured | TLS or SSL |
Port 25 also exists but is often blocked for sending from apps, so stick to what your host recommends.
A concrete example
Say you run a small web design studio and want to pitch local vet clinics. You found 150 clinics, verified their emails, and wrote a short three-step sequence. (If that niche interests you, here is how it looks for veterinarians.)
Your business email runs on a regular hosting provider, not Gmail. So you:
- Log in to your host and find the outgoing server details: host, port 587, your address as username.
- Check whether your host requires an app password for third-party tools, and create one if so.
- Confirm your domain has SPF and DKIM records set up for that host.
- Enter those details in your outreach tool and send a test email to yourself and to a friend on a different provider.
- Start small, for example 20 to 30 emails a day as a cautious rule of thumb on a mailbox that hasn't done outreach before, and increase slowly.
In GetClient, this is the "connect an SMTP account" step. You can connect any SMTP account or your Gmail accounts, then build the sequence in the flow builder (see the visual campaign builder explained) and set daily send limits by weekday so you stay inside your host's caps.
Common SMTP mistakes
Using your main domain for heavy cold outreach. Many senders set up a separate, similar domain for outreach so a reputation problem doesn't touch invoices and client mail. Worth considering before you scale.
Skipping SPF, DKIM and DMARC. SMTP will happily send without them. Receiving servers are less happy to accept. Set them up first.
Ignoring the provider's sending limits. Hosts publish or enforce daily caps. Find yours and set your tool below it.
Using the wrong port or encryption pair. Port 587 usually goes with STARTTLS/TLS, 465 with SSL. A mismatch gives connection errors that look mysterious but aren't.
Sending to unverified lists. High bounce rates are a strong signal to providers that something is off. Verify addresses before a campaign, and be careful with role-based emails like info@ that may go to a shared inbox nobody watches.
No way to opt out. Include an unsubscribe link and honor it. Rules on commercial email differ by country, so check what applies to you. This isn't legal advice.
If your emails are being sent but performing poorly, the cause may be copy rather than SMTP. These cold email mistakes that kill replies are worth a read.
How SMTP differs from sending through Gmail directly
Gmail and Google Workspace accounts can be connected through SMTP or through a direct account connection. Either way, the same principles apply: your limits, your reputation, your domain records. The difference is mostly setup. A direct Gmail connection is usually faster to configure; generic SMTP works with almost any host.
You can also spread sending across several mailboxes, each with its own modest daily limit, rather than pushing one account hard.
What to do next
- Find your email host's SMTP settings and write them down.
- Check your domain's SPF, DKIM and DMARC records.
- Decide whether outreach goes from your main domain or a separate one.
- Connect the account to your sending tool and send test emails to a few different providers.
- Start with a small daily volume and watch bounces and replies.
Once you're sending, keep an eye on results. If opens are weak, look at how to fix a low open rate. New GetClient accounts get 100 free credits with no card needed, and plan details are on the pricing page.