Need Clarification on Using Server Addresses -UPDATED

[BobH]

I need lessons on how email works. I guess I don't know as much as I thought I did.

Here's my assumptions: 1) Mail servers associated with ISP account connections use their POP addresses to route outgoing mail. The POP server either forwards it (I think this is called 'Relaying') to other mail servers or sends it to clients that are logged into that POP server. 2) Mail servers receive email at their SMTP server addresses from accounts logged into those addresses (for origination validation) then forward (or 'relay') messages to addresses in the mail header. Sometimes this would entail sending the mail to their own POP server and sometimes to other mail servers at other domains.

How am I doing so far?

If my assumptions are correct, what would the ISP mail server do with messages from a logged-in client if the SMTP server address were not local but that of another domain?

I have an ISP account that I use for Net connections and mail servers. I also host a web page that gives me email addresses and provides both POP and SMTP server addresses. I set up special email accounts in different email clients (Thunderbird, Outlook, OE). I use the ISP server addresses for most of my email; but when I set up accounts associated with my web page domain name, I used their POP and SMTP server address names. All the accounts are set up with no problems. When I choose OE and use an account set up with the web host domain mail server names (not my ISP's server names), the mail goes to the Outbox and is whisked away on the next Send execution - without any evidence of error.

I have run numerous tests and get the same results: messages appear to have been sent successfully (no error message; no returned mail messages over time) but the messages never arrive at their destination addresses. I've tried using recipient email addresses that are associated with both my ISP's mail server addresses and ones associated with my web host server addresses. It appears that anything originated using my web host server SMTP addresses fall into the bit bucket.

Anyone care to take on the daunting challenge of educating this old man?

UPDATE:
After continued attempts, I finally started uncovering the error messages coming from my ISP. They are 553 errors indicating to me that they are not allowing me to relay mail via their SMTP server. I am trying to get an answer from my ISP to find out if they will authenticate my identity using the POP data and relay my mail. Does this sound like I understand the situation?

[StuartR]

POP3 is used for incoming mail only. Email is received by the POP3 server and your email client then fetches a local copy of the email from the server, this usually causes the server to delete its copy of the email - but that behaviour can be changed with a parameter setting.

SMTP is used for outgoing mail only. Your email client connects to the SMTP server and sends the email, the POP3 server is not involved in this exchange.

Because of the issues with SPAM there are often restrictions on what SMTP server you can connect to. Some ISPs will only allow you to access their SMTP server if you have connected to the internet using their connection. Other ISPs will allow you to give a username and password to connect to the SMTP server. Some ISPs will prevent your PC from connecting to port 25 on a server that is outside their network, so you have to use their SMTP servers, or get an external SMTP server that uses a non-standard port number.

[BobH]

Thanks for the response, StuartR!

You confirmed my basic understanding of the functions of POP and SMTP servers at my ISP, and I've become a bit better educated about why my ISP might not want to use an SMTP server name in messages that it handles. What I remain unclear about is, when I log into my ISP's servers, I am authenticated by the names and passwords that are set up within my local email client software do, why does the ISP not 'know' me and have me authenticated sufficiently to allow me to originate messages using the SMTP server name of my web hosted servers. Does this question even make sense?

I have a query pending with my ISP but am not sanguine about their ability to understand my questions. Their phone support and chat support seem to be worsening.

[DaveA]

Here are the setting for Comcast, but other are similar. http://customer.comcast.com/Pages/FAQVi ... -for-email" onclick="window.open(this.href);return false;
Look at steps 9 and on about settings of the "Server" and "Advance" tab. You will need to get with the email provider for the correct Port number, and the "Authentication" is needed by most all of the email providers when you are NOT using their internet connection.