Is SMTP port 587 or 25?

What is port 465 for SMTP?

In all likelihood it is not a popular destination for mail, however it is the default destination for port 465.

I think there are at least a couple of reasons why this would be the case: It is the old and well-known standard. The first SMTP (email) protocol for sending email is from the 1980s. It had a number of security problems and most SMTP servers used an SMTP-over-TCP option instead. In effect port 465 is still reserved for the use of the SMTP-over-TCP option. A server like mail.yahoo.com won't respond to SMTP client requests on port 465 because they are not supporting the SMTP-over-TCP option. It's a legacy protocol that has fallen out of use. The SMTP-over-TCP option also has limitations compared to the modern STARTTLS SMTP client and server protocols.

The modern STARTTLS SMTP client protocol has many security advantages and doesn't have the limitations of SMTP-over-TCP. To use SMTP over TCP you need to explicitly enable it by passing a "-t" flag to the SMTP client.

Mail senders aren't required to send via SMTP-over-TCP. Many do. The majority of mail servers will tell clients to use the mail submission mechanism for security, rather than accept SMTP-over-TCP connections. The major exception being mail. I believe it supports both methods of submission for a while now.

SMTP-over-TCP has problems when dealing with a variety of MTAs because they are not designed to handle security and authentication properly. If you use SMTP-over-TCP on a shared mail server where every client that wants to submit messages connects to that mail server then you get into a situation where all messages can be captured. If that shared mail server is accessible from the Internet via the normal port then all you need to do is open port 465 to the world and you're in deep water. (The usual solution for this is to disable the insecure submission method altogether but that makes the entire SMTP-over-TCP transport method useless for that application.)

For the reasons above I think it is unlikely that port 465 is ever really used as the SMTP client port.

Is SMTP port 587 or 25?

I am trying to send mail from a website hosted on a home server.

I have it hosted on a different IP from the one I use for my actual server and from what I understand it should be on port 25 since that is the standard port for an SMTP server.

If I try to send mail with the smtp command it sends it to the address I want it to go to, but I get a message in my email saying there was a problem sending the email. If I use telnet on port 25 and type 'HELO test' into it, I get this error: Trying 50.19.167.

Connected to 50. 220 vps.example.com ESMTP Postfix (Ubuntu)
250 vps.com> 250 2.0 OK Sender
RCPT TO:
DATA. 354 Enter message, ending with "." on a line by itself To: user@example.com Subject: test.0 Message accepted for delivery QUIT. Connection closed by foreign host. I'm not sure what is going on. It doesn't look like I am getting a connection refused error either since I'm not getting any errors in my email. I have port 25 open to the world but it is closed for inbound connections. ?

The problem was that I had set my IP address to the IP address of my VPS. I was using the IP address of the host I used for my server when I was trying to send the email.

Is SMTP 25 TCP or UDP?

When setting up my server for hosting email, I have to decide which protocol to use.

I've been using both UPNP and TCP but found out that it was using TCP/25, when I should have been using TCP/2540.

How can I find out if I am using the wrong protocol? Should I be using UDP instead? UDP is a lower level protocol and is not recommended for use as a transport layer protocol. See this document on the subject.

So, you should use TCP or the related variants: TCP/1, TCP/25, TCP/50, TCP/75, TCP/125, etc.