What are MUA, MTA, MDA? (Was Re: Linux Mail Client)

[David Teague <dbt@elentari.cs.wcu.edu>]

On Wed, 23 Aug 2000, John Pearson wrote:
[snip]

> I differentiate between MUAs, MDAs, and MTAs; examples are:
>   MUA:  mutt
>   MDA:  procmail
>   MTA:  exim

John,
 
1) What do MTA, MUA, MDA stand for?  

I know that mutt is a mailer, not unlike exim and smail, but has
other functionality. procmail filters mail, but what else? exim
seems to be a drop in for smail and sendmail, so has similar
functionality.

2) What are the words for these acronyms? I have a bit of the
answer:

MTA is probably Mail Transport Agent (guess).  MDA is Mail Delivery
Agent. (from procmail man page, I can guess it delivers mail) 

man mutt doesn't tell much and there no exim man page on my system.

What is MUA?

3) What is the function of these?

4) Where would I look this up? What is TFM  I should R? 

--David
David Teague, dbt@cs.wcu.edu
Debian GNU/Linux Because software support is free, timely,
                 useful, technically accurate, and friendly.