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MTA and SMTP server

Posted on 2011-02-14
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Last Modified: 2012-05-11
Hello,

I've a stupid confusion, when we say an MTA (mail transport agent) and MDA (mail delivery agent) are responsible for delivering and storing mails then what SMTP server does?
Does an MTA uses SMTP protocol to send
or
uses an SMTP server that finally sends the mail on request of an MTA or MUA?

PostFix and Sendmail are two implementation of MTA, what are the examples of SMTP server software?

A link to some article that explains all this well, will be a great help.

Thanks
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Question by:rajoo_sharma
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by:nasirbest
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Don't mess SMTP with MTA or MDA, SMTP is a protocol stander and later are server things, MTA "speaks" SMTP to send or receive new e-mails. it is just like that you are an Indian but speak English to convey your message
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by:nasirbest
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Every MTA including PostFix and Sendmail uses SMTP as basic protocol.
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by:rajoo_sharma
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Thanks Nasir,

Thats a good explanation and I understand Protocol(s) in general. What appears ambiguous to me is:
1. When you say you've an SMTP server on a local machine which is connected to the Internet and you can send mails using a scripting language e.g. PHP / ASP.
Now in this case PostFix or Sendmail is not installed on this machine, so when MTA is comes into the picture when you are sending the mail?


2. When you have an MUA (Mail User Agent) e.g. Outook, you can send mail by setting SMTP address and Port in it. Is this mail routed from our MTA Server?

3. And SMTP is a protocol, so what exactly an SMTP Server is?

4. And what is an SMTP client? the MUA program?

Thanks
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ajaykerala earned 450 total points
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MTA - message transfer agent

MUA - mail user agent, example outlook

SMTP - Simple Mail Transfer Protocol

MSA - mail submission agent

MSA or MUA send out a email it is transmitted using Simple Mail Transfer Protocol (SMTP) by MAS or MUA, when the message is being relayed(transmitted) using smtp its forwarded to a message transfer agent, every mail server has a MTA agent which is associated with the mx records of the domain. you can get detailed information at http://en.wikipedia.org/wiki/Message_transfer_agent

let me know if this helps you
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by:ajaykerala
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by:rajoo_sharma
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Thanks Ajay,

The Pic explains the process very well,

1. When you say you've an SMTP server on a local machine which is connected to the Internet and you can send mails using a scripting language e.g. PHP / ASP.
Now in this case PostFix or Sendmail is not installed on this machine, so MSA / MTA not required in this setup?

2. And SMTP is a protocol, so what exactly an SMTP Server is?

3. And what is an SMTP client? the MUA program?

Thanks
0
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Author Comment

by:rajoo_sharma
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Hello again,

The wiki link http://en.wikipedia.org/wiki/Mail_relay clears my doubt as it says "An MTA implements both the client (sending) and server (receiving) portions of the Simple Mail Transfer Protocol."

So I'm left with last confusion from my previous comments:

When you've an SMTP server on a local machine which is connected to the Internet and you can send mails using a scripting language e.g. PHP / ASP.

What happens in this case?

Thanks
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by:ajaykerala
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When you've an SMTP server on a local machine which is connected to the Internet and you can send mails using a scripting language e.g. PHP / ASP. - yes you can :) use the cdont or the php mail.. make sure the smtp is running in the IIS for the mail to be out.
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Author Comment

by:rajoo_sharma
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Hi Ajay,

This is what my question is, if I can send mail from a local machine having SMTP (with IIS 6.0) then should I consider this SMTP as a local MTA?

Thanks
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by:ajaykerala
ajaykerala earned 450 total points
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yes. IIS SMTP is a powerful MTA
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Author Comment

by:rajoo_sharma
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great, thanks Ajay.
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by:ajaykerala
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u r welcome
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Author Closing Comment

by:rajoo_sharma
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My confusion is over...
Thanks
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