Email

From Docunext Technology Wiki

Good old spam, I mean email. Its funny, but for users, email is convenient and simple. For systems administrators, email can be incredible complicated and frustrating.

My Email Services Configurations

I had originally included it here, but it became too big a beast.

Protocols

IMAP Email - port 143 and 993 for tls
POP Email - port 110 and 995 for tls
SMTP Email - port 25 and 587

Email Applications

IMAP / POP Email Servers

SMTP Servers

Email Clients

Free Webmail Services

Mailing List Software

GNU Mailman

Email Proxies

Miscellaneous Email Software

IMAP or POP3?

I use the server to store messages, and one can do so with either POP3 or IMAP. IMAP does this natively, but it can be a little slow. With POP3, the messages are completely downloaded and stored on a computer, in that case, I explicitly set the POP3 client to keep the messages on the server, otherwise they will be only stored on the computer. With that setup, the major difference is that changes made on the client (like making new folders), won't be reflected on the server when logging in via webmail or another IMAP client.

Bring It Together

How do I try to get SMTP, POP, and IMAP servers, as well as web and desktop clients to all get along, AND fight the good battle against Spam? Its a good question. Here's some of my notes:

I have a few Postfix servers setup, but only one is setup to deliver mail to user mailboxes. The others are setup as relays, for those users. In the event the delivery server is unavailable, the relay servers can be used by clients to send outgoing mail. In that scenario, if the POP / SMTP servers are available even though the main SMTP server is unavailable, then the sent mail will still get copies to the user's "Sent Messages" folder. In that case, most SMTP clients don't play well with multi-homed SMTP hosts (one hostname with multiple A record IP addresses), and I setup a failover with the firewall. If the client is web-based, it might be a different story, as setting up a failover for the localhost doesn't make much sense. I think in that case it might make sense to failover the web app, which would migrate the smtp server to the new machine, but you could point the IMAP server to the primary IMAP.

The fight against Spam:

* DNSRBL
* Greylisting
* Rules based filtering

See My Email Services Configurations for a more in-depth look into how I setup my email servers.

Summary of Packages

Miscellaneous Email Topics

Email Problems

There are many problems associated with email:

External Links