Can't send email from your email app
When your email app receives messages but fails to send them, the problem is almost always in the outgoing side of the setup. This guide is for anyone using an email app such as Outlook, Apple Mail or Thunderbird, or the mail app on a phone, who sees sending errors or messages stuck in the outbox. If messages leave your app but never arrive, see Email not arriving instead.
How sending works
Email apps use two kinds of connection. IMAP or POP collects incoming mail. SMTP (Simple Mail Transfer Protocol) sends outgoing mail through your provider's outgoing server. Each has its own server name, port, encryption setting and sign-in. Receiving can work perfectly while sending fails, because the two settings are separate. IMAP, POP and SMTP explained covers the difference in more detail.
Read the error message
The error tells you which part failed.
| What the error says | Likely cause |
|---|---|
| "Cannot connect", "connection timed out" or "server not found" | Wrong server name or port, or the port is blocked on your network |
| "Authentication failed", "535" or "username and password not accepted" | Wrong password, or authentication is not turned on |
| "Relaying denied", "relay access denied" or "554" | The app is not signing in to the outgoing server |
| "Certificate" or "secure connection" errors | Encryption setting does not match the port, or the server name does not match the certificate |
| "Mailbox full", "quota exceeded" or "account suspended" | Account status or limits |
| A bounce message saying the message was rejected for policy reasons | The receiving server refused it; see Email not arriving |
Check the outgoing server settings
Open the account settings in your email app and find the outgoing server, often labeled SMTP. Compare each value with the settings your email provider publishes.
- Server name: exactly as your provider gives it, for example
mail.example.com. A typo or an old server name is a common cause. - Port and encryption: these must match each other.
| Port | Encryption setting | Use it? |
|---|---|---|
587 | STARTTLS (sometimes shown as TLS) | Yes, the usual choice for email apps |
465 | SSL/TLS (implicit TLS) | Yes, if your provider supports it |
25 | None or STARTTLS | No: meant for servers passing mail between each other, and often blocked |
Use whichever of 587 or 465 your provider recommends, with the matching encryption.
Turn on SMTP authentication
Your outgoing server needs to know it is you before it sends mail. This is called SMTP authentication. In your email app, look for an option such as "My outgoing server requires authentication" and turn it on.
In most setups, use the same username and password as for incoming mail, usually your full email address, such as jane@example.com. If your app offers "use the same settings as my incoming server", that option is normally correct.
Port 25 is blocked on many networks
Many internet providers, hotels, offices and public Wi-Fi networks block outgoing connections on port 25 to reduce spam from infected computers. If your app uses port 25, it may work at home and fail elsewhere, or not work at all. Switch to 587 or 465.
To test whether your network is the problem, try sending from a phone on mobile data, or from another network. If that works, your usual network is blocking or interfering with the connection.
Check your password and account
- Password changed recently? Update it in every app and device that uses the account, including the outgoing server settings, which some apps store separately.
- Too many failed attempts? Some providers block sign-ins for a while after repeated wrong passwords. Fix the password everywhere, then wait or ask your provider to check.
- Mailbox suspended or over its limits? A full mailbox, an unpaid account or a sending limit can stop outgoing mail. Sign in to webmail, if your provider offers it, and try to send from there. If webmail sends but your app does not, the problem is in the app's settings. If webmail fails too, contact your provider.
Step by step
- Note the exact error message and when it started.
- Try sending from webmail. This tells you whether the account itself can send.
- Check the outgoing server name, port and encryption against your provider's settings.
- Make sure SMTP authentication is on and uses the same username and password as incoming mail.
- Re-enter the password, in case it changed or was saved incorrectly.
- Try another network, such as mobile data.
- If nothing helps, remove the account from the app and add it again with the correct settings. See Set up email on your devices.
For the correct settings for your DomainPilot business email, see the DomainPilot email setup guide. If sending still fails, contact DomainPilot support with the exact error message.