6
4
Normally in a email client you need to configure an SMTP server to use to send mails. When you send a mail, your configured SMTP server simply resolve the domain after the @at in the email address of the recipient with a DNS request of type MX. The DNS will answer with the address of the mail exchanger SMTP server of the recipient's mail provider, and your SMTP server will forward your mail to it.
My question is: why this is not done directly by the mail client? It is nothing special: it is just a DNS mx request and the protocol do deal directly with the mail exchanger of the recipient provider is alaways SMTP.
If it were so, the mail could go directly to the right server: it should be faster and avoid useless traffic.
May this be due to the fact that maybe the recipient's SMTP server could be down for some reason or too busy to process the mail when you send it, and that therefore the advantage of use our personal SMTP server is that it takes care to try again to send the mail at regular intervals?
This is the only reason I see: actually it would be not so practical if this would be responsibility of the mail client, since maybe the user close it or shutdown the computer.
If this is the only reason: does it happen so often that an SMTP server is unable to process an email immediately?
This is a really terrific question! I'd love to know the same thing. Thanks for asking! – murftown – 2014-06-25T21:40:36.887
1Why because its faster to have the actual server that is sending the email to forward the data to the recipient's server. – Ramhound – 2014-05-15T13:00:17.097
1Why faster? You are adding an hop, a possible bottleneck, in the best case the time required is the same, but adding a hop in the route of the mail in my opinion is very likely to require an higher amount of time – WoDoSc – 2014-05-15T13:02:31.453
Besides you dynamic IP address is likely to be blacklisted for SPAM. So the target SMTP server (if properly configure) is going to reject your mail. – drk.com.ar – 2014-05-15T13:22:20.030
1@drk.com.ar Ok I See your point, but if your IP is in a black list, 'conceptually' it should be rejected by any server, i.e. including your SMTP server and not only by the recipient SMTP, so this is a related problem but I don't see that is the main reason. – WoDoSc – 2014-05-15T13:26:06.473
1Usually you have authentication in your SMTP server. And typically you are going to use submission port 587 instead of 25 for sending mail. – drk.com.ar – 2014-05-15T13:44:50.917
@drk.com.ar ok so basically if you have an SMTP that trusts you (through authentication) you can use it as a 'proxy' in case your IP is for some reason blacklisted by the recipient SMTP. But this is a problem about the (ab)use of the protocol, not the protocol itself. It is like to say that you need ALWAYS to use a proxy/VPN to navigate through the web because your IP could be banned by some site for some reason. – WoDoSc – 2014-05-15T14:08:24.177
Today most dynamic IP ranges are blacklisted or distrusted. But the actual use of SMTP (in the past) is about the message delivery system. You can't expect the final SMTP server to be always online. Or the recipients inbox to be always available. SMTP protocol has a lot of instances where the server keeps trying to deliver during hours or days. – drk.com.ar – 2014-05-15T16:11:31.687
SMTP simply doesn't work this way. See RFC2821 for clues.
– milli – 2014-05-21T23:39:55.287