On Tuesday 29 June 2004 14:43, Graham wrote:
(Silly answer coming up...) I hesitate to jump in with so many people around who know what they're doing, but I'm not sure what benefits there are - for a domestic user - in running incoming SMTP as opposed to simply having your server collect mail from your ISP using fetchmail then distribute it to local users via Postfix. This way it doesn't matter if the server or ADSL go down from time to time. You don't even need a fixed IP address, for that matter. All I need one for is to host a couple of webservers that don't carry anything critical but allow me to do server-side processing my ISP wouldn't support.
SMTP has a few advantages, most of which only become relevant as you scale things up.
Firstly, you are in control of what mail you accept, you can bounce people based on blacklists, domain resolution or because you don't like the sound of their name. This makes sense because you are not wasting bandwidth downloading mail you don't want to receive.
You are not dependant on your isp's mail relay, Anybody here who is on Demon for example can verify how annoying it is to have delayed or lost mail as a result of your ISP's SMTP service not responding in a timely fashion.
By having an MX record pointing at your IP, it becomes easy to send mail directly from your system rather than via your ISP's relay without falling foul of name lookups.
Also because you are in full control, you can assign any domain you control to your system simply by getting an MX record added to that domain, with pop if you wanted to accept mail for foo.com then you would either have to set up a forwarding service to an existing account, set up an POP/SMTP service at a hosting provider or negotiate with your ISP to accept mail for that domain and route it to your account for collection.
A short tutorial from one of the IT experts would be most interesting. Like, what is a secondary MX provider or reverse DNS and why would we need it? Apologies for such green questions but most of what I read might as well be Sanskrit for all the practical help it gives me.
Secondary MX is a fallback system, if you have an MX record pointing at your own system and then for whatever reason your system is unable to accept mail then any senders will either get an Non Delivery Report or the mail MAY get queued to be resent later. When MX records are attached to a domain they include a priority number, the highest priority (lowest number) gets tried first and if that fails a correctly configured mail system will attempt delivery to the next one on the list. So you have an alternative transit that can hold your mail until your system it able to accept it. As has been pointed out it is best practice that the fallback is somewhere completely independent of your connection and your ISP. Although Richard has made some good points about how this can be a disadvantage.
Reverse DNS is exactly what it says on the tin, a DNS lookup resolves a domain to an IP, a reverse DNS resolves an IP to a Domain, Mail systems may use Reverse DNS to confirm that the sender is really the Domain that they say they are. This essentially stops you receiving mail from a zombied Windows machine somewhere that is being used as a spam relay, unfortunately it can also stop you receiving mail you want as not everybody takes care to sort their reverse lookups out. (actually the way DNS and particularly reverse DNS works is pretty clever and fairly interesting)
W