Default ports for email protocols

Here’s the list of three most common email protocols and their default ports:

* Check the differences between POP3 and IMAP

** SMTP (and port 25) was originally designed for email transfer, not submission. So yet another port (587) was defined for message submission.

Establishing connection using default port is easy:

// C#

client.Connect("mail.example.com");

' VB.NET

client.Connect("mail.example.com")

If you need to specify different port, just use overloaded version of the Connect method:

// C#

client.Connect("mail.example.com", 999);

' VB.NET

client.Connect("mail.example.com", 999)

Implicit SSL/TLS mode

Establishing connection encrypted with SSL/TLS using default port is easy:

// C#

client.ConnectSSL("mail.example.com");

' VB.NET

client.ConnectSSL("mail.example.com")

If you need to specify different port, just use overloaded version of ConnectSSL method:

// C#

client.ConnectSSL("mail.example.com", 999);

' VB.NET

client.ConnectSSL("mail.example.com", 999)

Explicit SSL/TLS mode (aka TLS)

Sometimes your server might require that you first connect on non SSL/TLS (plain text) port using regular Connect method, and then start SSL/TLS negotiation using STARTTLS (or STLS in case of POP3) command. This is called explicit SSL/TLS mode and sometimes is referred to as TLS:

// C#

client.Connect("mail.example.com");
client.StartTLS();

' VB.NET

client.Connect("mail.example.com")
client.StartTLS()

Here you can find more details on SSL vs TLS vs STARTTLS and STLS.

Self-signed certificates

Remember that you can ignore SSL/TLS certificate errors (for example when your server uses self-signed certificates) using ServerCertificateValidate event:

// C#

client.ServerCertificateValidate +=
    (sender, e) => { e.IsValid = true; };

' VB.NET

AddHandler client.ServerCertificateValidate, AddressOf Validate

Private Sub Validate(ByVal sender As Object, ByVal e As ServerCertificateValidateEventArgs)
    e.IsValid = True
End Sub

Tags: C# IMAP POP3 SMTP SSL TLS VB.NET