I just set up a mail server but it doesn't work because my ISP blocks all the ports used for a web server and also mail server on their end (my modem does not have a router built-in). How do I not use the default ports like 25, 110, etc. for all my mail server programs so I can change the ports they use? I followed this guide on Ubuntu: http://flurdy.com/docs/postfix/

Also, if I do change these ports, will it affect my mail users? On Apache, I was able to change the default port 80 in the config to port 8080 and my website worked when someone else went to my domain address. If a user goes to my website and logs in to their e-mail (SquirrelMail) and sends an e-mail to someone like @gmail, will using different ports matter? (I run my own SMTP server.)

Set the port in an smtpd entry in the master.cf file.
For example

225 inet n - n - - smtpd

I got that, but now I can't receive e-mails because other e-mail services do not know to send e-mails to me @ port 225. Is there any other default SMTP port besides 25 that all e-mail services know to send to? Like most browsers know to check port 8080 as well as 80 for http servers (which is how I got my website working since my ISP blocks port 80. I just used port 8080 for my Apache web server and now everyone can see my website). So when other people send e-mails to my server, since port 25 is blocked, what other ports will they be trying to send through to?

some use port 2525, or 465 as for ssl, but I do not think that solves your "problem"

otherwise there are service like
h_t_t_p://www.smtpport.com/

That costs money though and I don't have any of that. I've set up everything so far for free (I even got the server for free) but for this mail thing, I have to purchase a relaying service? I have about 100 people using my mail server but they can't receive e-mails.

Note that firstly, you're violating your ISP's terms of service (TOS) and this *can* get you into trouble.

With this in mind, Dyndns.com has a free mailhop service designed to circumvent TOS.

It will reroute mail to whatever port you choose.

There is, however, the other issue that many places will block a mail server in an ISP's address block, because it's so often used for spam. For example, my own ISP has a somewhat nebulous TOS, where it's not specifically prohibited, but one is not supposed to use excessive bandwidth. So, I can more or less run a mail/web server as long as it's not used much.

However, many places will block it because it's in a dynamic ISP block.

I believe DynDNS's mailhop service costs money

Hrrm, it used to be free. (I think)

However, I see you are quite correct.

Does MX records have anything to do with this?

I don't understand it completely..

Dave

It's not simple, seriously. An MX record is the where the mail goes for a domain.

See if this explanation makes sense.

http://bobcares.com/blog/?p=29