What is SMTP?

SMTP stands for Simple Mail Transfer Protocol. It is the protocol used for sending email messages between mail servers.

Most email systems that send mail over the Internet use SMTP to send messages from one server to another. Email clients can then retrieve messages using an email download protocol such as POP3 or IMAP.

SMTP is also generally used to send messages from an email client to a mail server. This is why, when configuring an email application, you need to specify both the incoming mail server (POP3 or IMAP) and the outgoing mail server (SMTP).

SMTP Settings

When configuring your email application, use the settings below depending on whether your mailbox is configured as POP3 or IMAP.

POP3 Settings

Use the following settings if your email account is configured as POP3:

Username: Your full email address
Password: The password for your email account

Outgoing Mail Server (SMTP): mta.extendcp.co.uk
Outgoing Mail Server Port: 587
Encryption: STARTTLS
Authentication: Password

Incoming POP3 Server: pop3.extendcp.co.uk
Incoming POP3 Port: 995
Encryption: SSL/TLS
Authentication: Password

IMAP Settings

Use the following settings if your email account is configured as IMAP:

Username: Your full email address, for example [email protected]
Password: Your email password

Outgoing Mail Server (SMTP): mta.extendcp.co.uk
Outgoing Mail Server Port: 587
Encryption: STARTTLS
Authentication: Password

Incoming IMAP Server: imap.extendcp.co.uk
Incoming IMAP Port: 993
Encryption: SSL/TLS
Authentication: Password

Alternative SMTP Port

If STARTTLS is not available in your email application, but SSL/TLS is available, select SSL/TLS and use port 465 for the outgoing mail server.

Outgoing Mail Server: mta.extendcp.co.uk
Port: 465
Encryption: SSL/TLS
Authentication: Password

SMTP Authentication

The outgoing mail server requires authentication.

If your email application provides an option such as “Outgoing server requires authentication” or “Authenticate SMTP server”, make sure this is enabled.

Enter the following:

Username: Your full email address
Password: Your email password

If the application provides an option to use the same username and password as the incoming mail server, this can be selected.

Due to increasing security standards many mail providers are now marking unauthenticated messages as spam or rejecting them altogether. If you're sending via PHP mail or through an SMTP method without using an actual mailbox to authenticate, the emails might send but fail to reach the recipient reliably.

To ensure consistent delivery of messages like order confirmations and form submissions, we recommend setting up a proper mailbox (e.g. noreply@) and using SMTP authentication through that account. This allows the mail to be sent as fully authenticated, improving deliverability across all major mail providers.

Important

• Make sure your full email address is entered as the username where required.
• Make sure the correct email password is entered manually in all required password fields.
• The outgoing mail server must be configured to use SMTP authentication.
• For SMTP, use port 587 with STARTTLS where available.
• If STARTTLS is not available, use port 465 with SSL/TLS.
• For POP3, use pop3.extendcp.co.uk on port 995 with SSL/TLS.
• For IMAP, use imap.extendcp.co.uk on port 993 with SSL/TLS.

Article ID: 571
Created On: Tue, Mar 31, 2015 at 4:56 PM
Last Updated On: Tue, Sep 8, 2026 at 6:03 PM

Online URL: https://www.heartinternet.uk/support/article/what-is-smtp.html