the mail trail...sendmail

[Sean O Sullivan]

rado wrote:

>hi Y'all,
>Oh, I am guilty of running programs that I don't know exactly what
>they/their job is in the total process.
>I'm talking about the mail system I have set up.
>I just have a basic sendmail/procmail/evolution pop setup.
>I want to know exactly what sendmail's job is. The man sendmail page
>says it's job is to sendmail, as the name implies. Please tell me if my
>thinking is warped. I think sendmail sends the mail in both directions.
>you write a msg, it goes to sendmail and it gets sent on the way. 
>a msg comes in sendmail is listening on, think it's port 25. sendmail
>grabs it and.....
>  
>
Sendmail sends mail & receives mail on port 25, as you have said.
It also handles delivery of mail (i.e. puts new mail in /var/spool/user)

>Here is where I am hung up. What actually takes place now? 
>In just a basic, Sendmail system w/out many changes at all that came
>stock w/FC3, can I assume that: Say a msg comes in for rado, does it go
>to var/spool/mail/rado?  
>  
>
yes

>when exactly does procmail get in the game?
>I notice that in /home/rado there is lots of stuff concering mail.
>  
>
procmail is for setting filters
i.e. setup a filter so all mail which is addressed to 
fedora-list at redhat.com gets put into a different folder/file

>~/Mail, ~/mail, ~/.evolution.
>  
>
. folders in your home dir, are hidden folders, and usually used for 
user settings

>I really don't want to get too, too, tech here, just a little
>understanding of where the mail trail goes and how to follow it.
>
>  
>

You send mail ...
you type your mail etc, and if your smtp server is set to localhost ... 
then it connects to sendmail server, tells it who mail is from, who it 
is for, and then if their accepted, gives the message subject/body.

sendmail, if all is correct etc, will then lookup the MX record for the 
domain your sending to (i.e. if your sending mail to user at example.com, 
it looks up the MX record for example.com (nslookup/dig)) and connects 
to that address on port 25, telling the remote server who it has mail 
for, and who it's from etc.

the RFC on SMTP is quite handy to read, not too bad a read.

Regards,

Sean