possibly a stupid question
but i'm a complete noob in email matters..

so i want to set up an email server both to receive and send emails.
I also am on a dynamic ip scheme with my ISP.
I do have a dynamic dns account with no-ip.org

the Questions are:

-will somebody be able to send emails to me at the <user>@<dyndns_name>.no-ip.org email address?
-will I be able to send emails from the <user>@<dyndns_name>.no-ip.org email address?

I know i'll be able to login to accounts like gmail and yahoo and download emails from there.. but even that i don't know - even macroscopically how its done:

-is it the sendmail deamon that accepts the mail from <me>@gmail.com, <me>@yahoo.com, <me>@<dyndns_name>.no-ip.org?
-is it the sendmail deamon that does the sending of email (as well)?
-can it push emails that I want to send as <me>@gmail.com to the gmail smtp servers (and they in turn will push my email even further)?
-can it push emails from <me>@<dyndns_name>.no-ip.org to receipients??
and finally,
-WILL receiving pop/imap servers allow incoming email from my server? or due to the dynamic ip they'll assume I'm a spam server?

Any guides and pointers into clarifying things before I start tweaking will be greatly appreciated!

Thank you
Nass

- probably, unless your ISP blocks it. In principle it should be fine, as long as the appropriate DNS records hit your IP.
- yes, but many other ISP's might think you're spam if you don't do things like use SPF records and use your ISP's own upstream mail relay host.

- yes, IF you choose to use sendmail. I'd suggest postfix instead.
- yes, SMTP servers accept and forward on mail between themselves until they reach a destination
- you wouldn't send them via gmails servers, but an smtp server can send an email from any address you feel like, they don't care.
- yes
- pop3 / imap servers are for users to download emails, they do not receive email.

well common sense makes me conclude that ISP mailservers, will NOT forward traffic that is not part of their domain. ie the <me>@dyndns will not be fwd but my ISP mailserver.. is that a faulty conclusion?

Also I am reading about SPF records, but it doesn't state anywhere WHERE you are supposed to add the SPF configuration. In the sendmail configuration file? in the DNS table ?

I do not understand the difference...
I mean, the path of an email is: smtp server on senders end, going to smtp servers around the world, to reach an smtp (and then pop) or directly a pop/imap server at the receivers end?

SPF records are in the DNS records for the domain. The DNS record is implicitly correct, your server is not. So if your "correct" data says that your server is a valid source of emails for that domain, then they will be generally accepted, see?

The difference is that SMTP servers only do one thing really, they get given email, and then give it to someone else. Like people passing buckets of water to a fire, the guy at the end just has no one to give it to, so chucks it on the fire. He's still really doing the same thing though. Carrying on this stupid analogy, an IMAP / POP3 server would be more like the guy at the fire running off to get a bucket of water, finding one and bringing it back again. Then doing it again. Hope that makes sense.

SMTP servers and IMAP / POP3 servers have nothing in common, they do not know each other exists, and just conveniently know how to real the same email data, in a flat file etc.

Your ISP may accept mail relayed via your server as you will be connected to their physical network, but it may or may not require authentication. You should also check with your ISP's terms of service to see what their position is on running your own mail server. Some permit it, others don't. FWIW, I ran a mail server using a dynamic IP and a dyndns account for over a year with little to no trouble, so yes, it is do-able.