As an individual learns more about just how mail customers, SMTP servers, and the entire online mail system works, they may wonder regarding why an intermediate SMTP web server is even required. With that said in mind, today’s SuperUser Q&A message has the answers to a curious visitor’s questions.

Today’s Question & Answer session pertains to us courtesy of SuperUser– a class of Stack Exchange, a community-driven grouping of Q&A web sites.

Picture thanks to David Schroeder (Flickr).

The Question

SuperUser visitor Tobia needs to know why an intermediate SMTP server is required to send mail:

Why do I require an intermediate SMTP web server to send out mail? Why is my mail customer (Outlook or Thunderbird) not able to send out messages straight to the recipient’s SMTP domain name?

As an example, if I need to send mail to [email protected] with my Gmail account, I send it to the smtp.gmail.com web server; then this web server sends my message to the MX web server of example.com.

Why is an intermediate SMTP web server needed to send out mail?

The Answer

SuperUser factor davidgo has the response for us:

It is practically possible to send mail straight to the recipient’s SMTP server from your computer.

Considering it from a historic basis, if the remote SMTP server is down, you desire a system to automatically manage it and keep retrying, therefore you have an SMTP web server. Likewise, in the old days, not all mail servers were connected all the time (far away web links were costly), so mail would certainly be queued as well as sent out when a web link was developed.

Going on to where Internet solutions are cheap, it is still helpful to have devices to retry sending mail if a server is not available. It is not perfect for this functionality to be created into the MUA (Mail individual agent/end individual mail program). These functions fit into an MTA (Mail server/SMTP web server).

Yet it gets worse– spammers. Most mail (more than 80 percent) is spam. Mail providers do whatever they can to minimize this trouble as well as a multitude of techniques make presumptions about the means mail is supplied. The adhering to are essential considerations:

1. Greylisting: Some carriers will immediately go down a mail connection if the sender and also recipient have actually not connected before and also anticipate them to try a 2nd time. Spammers usually do not retry while an SMTP server is constantly expected to. This minimizes the quantity of spam by about 80 percent, but it draws to need to do this though.

2. Reputation: It is a great deal more likely that someone sending mail via a reputable, well-known SMTP web server is official contrasted to an unreliable web server. To get a feel for online reputation, providers do a number of things:

There are possibly other small problems, but these would be the major ones.

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