Problems

Email not delivering

If mailq reports email in the queue, use /usr/lib/sendmail -q -v to show you whats happening.

My new computer cant send email.

Probably because the host isnt in sendmail.cw read below.

I havnt recieved email for ages.

Check the sendmail process on the server and restart it if it has died.

Details

Email is stored on the server mail.earth.monash.edu.au and processed with:

sendmail
popd
imapd

IMAP

IMAP allows the user to read email from mail boxes stored on the server. IMAP allows reading a mail box from many locations and seperate computers. PLEASE USE IMAP!

POP

This protocol reads the email from the server onto the local machine and allows the user to read the email locally. It is bad because this means that you can not read email from multiple locations and if your client crashes then your email is lost.

Sendmail

Sendmail is responsible for delivering outgoing email, recieving email from outside and relaying email from desktop computers to its final destination.

Sendmail: delivering outgoing email

You can check the outgoing mail still in the queue with the command mailq. This will list the messages ID, size, and from/to information. The outgoing email is stored in /var/spool/mqueue in two parts, the Data part and the Queue information. A '*' next to the ID in mailq means that the mail item is locked and is being delivered now (or sendmail is attempting to deliver it).

You can force delivery of queue'd email with the command /usr/lib/sendmail -q -v which will give you debugging output of exactly what is going on.

Sendmail: recieving email from outside

The sendmail process opens TCP port 25. You can verify an email address by directly connecting to the port like so:

root@orion:/  # telnet mail 25
Trying 130.194.168.8...
Connected to orion.earth.monash.edu.au.
Escape character is '^]'.
220 mail.earth.monash.edu.au ESMTP Sendmail 8.9.3/8.9.3; Thu, 2 Nov
2000 15:42:20 +1100 (EDT)
vrfy cameron
250 
^]
telnet> q
Connection closed.

In the above example, I telnet'ed to the sendmail process and asked it to verify the user cameron.

You can locate the process running sendmail it with: ps -aef | grep sendmail. There should be atleast 1 sendmail process, more if it is currently trying to deliver or recieve email.

You can start and stop sendmail with sh /etc/init.d/mail start or sh /etc/init.d/mail stop. Stopping email will not cause any loss of email. Sendmail is paranoid about delivery.

Incoming email is stored in the users email box in the directory /var/spool/mail. This is a plain text file and can be edited to remove crappy attachments.

Sendmail: relaying email

When a desktop machine sends and email, it is delivered to sendmail on the mail server which must relay it to the correct destination. Sendmail will NOT relay email by default. Add a list of all client machines to the file /etc/mail/sendmail.cw to allow relaying from those clients.

Sendmail: sendmail.cf

Set Djmail.earth.monash.edu.au in /etc/mail/sendmail.cf to make sure all email goes out of the department as mail.earth.monash.edu.au rather than the local host name.

Sendmail: unix clients

Set DSmail.earth.monash.edu.au in /etc/mail/sendmail.cf to make sure all email is delivered to mail.earth.monash.edu.au for routing rather than being directly delivered by the unix client.