Connect a custom SMTP server
Use any other provider or your own mail server by entering its SMTP details.
If your provider isn't one of Mailbo's built-in tiles, use Custom SMTP. Any service that gives you SMTP details works — you just type them in yourself.
What you'll need from your provider
Find these four (sometimes five) values in your provider's dashboard, usually under "SMTP", "Sending", or "Integrations":
| Field | What it is |
|---|---|
| SMTP server / host | e.g. smtp.yourprovider.com |
| Port | usually 587 (STARTTLS) or 465 (SSL); 2525 is a common fallback |
| Encryption | STARTTLS (587) or SSL/TLS (465) — match the port |
| Username | provided by your service |
| Password | provided by your service (often an API key or generated password) |
Which port? Use 587 with STARTTLS by default. If 587 is blocked on your network, try 2525. Use 465 only if your provider tells you to use SSL.
Step 1 — Verify your domain with that provider
Almost every provider needs you to prove you own your sending domain by adding SPF and DKIM DNS records. Do this in your provider's dashboard first — see Verify your domain.
Step 2 — Enter the details in Mailbo
- Settings → SMTP & sending → click the Custom SMTP tile.
- Sender: From email (on your verified domain) + From name.
- Credentials: type the host, port, encryption, username, and password from above.
- Save, then Send test email.
Troubleshooting
| Problem | Fix |
|---|---|
| Can't connect | Wrong port/encryption combo — 587 = STARTTLS, 465 = SSL. Try 2525 if blocked. |
| Auth fails | Double-check username/password; many providers use an API key as the password. |
| Sends but goes to spam | Your domain's SPF/DKIM aren't set up — see Verify your domain. |
Still have a question?
Can't find what you need in this guide? We're happy to help.
Last updated 6/15/2026← More in Sending & Deliverability