If you are in a hurry, it's enough to skim over the terse commandments and stick to them. The remaining text just explains my perhaps odd preferences.
Send your email To: that list address, or send it to: me with a Cc: to the list. Whenever I send you an business email with a Cc: to the support address, keep the Cc: to my colleagues in your replies.
The reason behind those list addresses is to assure your prompt service even when your usual contact is ill, too occupied with other customers, or taking a vacation.
Hint: during my vacations, it is not my favourite pastime to check my email box and to relay messages to my colleagues. Please respect my time off. Thanks.
It works even better if you stick to the convention to pre-format your message to a line width smaller than 80 columns. (Or still better just 72 columns to give some room for quoting prefixes.)
Alternatively, if you prefer to send one really long line for each paragraph and expect me to reformat that, please follow RFC 2646/3676 (The Text/Plain Format Parameter).
And yes: It's YOUR job to come up with a legible message in first place. Don't expect all the readers to do the formatting you forgot. If you are a client: all extra-time I have to do to read your message will be billed.
You can rely upon me using a constant width font and standard tabs (which means: every 8th column).
Subject: =?iso-8859-1?Q?Anfrage=3AM=F6glichkeit_f=FCr_einen_Internetzug?=angthen this is your problem, not mine.
Only send Word files to me if you are willing to deal with nicely formatted replies from my side, coming in DVI or ditroff format.
If you ask me for some access password and security does matter (that's not always the case), just send me your public key. My public key is this one and is already registered with the pgp.net key server network. Small public endorsement: I do trust the escape e.V. Certification Authority. I convinced myself that they stick to thorough procedures. Most important, they are competent enough to ensure to know what they are actually doing, not just some droids which are easily betrayed.
For larger lists: make sure your list maintains some standards of decency. (To be extended. In short: Don't mess around with "From:"/"Reply-To:"/"Message-Id:" headers. Do your best to prevent spam. Educate mailing-list members with ill vacation auto-replies. Mark list messages so they can be recognized. Include unsubscribe directions with each message.)
In order to be able to read and work on my/your email from anywhere, I restrict myself to absolutely portable (read: stone-aged) mail interfaces.
If you absolutely need to know: I usually use good ol' "mailx" through a telnet session. This works at the office, at home, and abroad. It works through firewalls, it works on a dinky palm. Yes, I used elm/mutt/rmail/vm/netscape-messenger/thunderbird/outlook before. mailx does the things I need, protects me from virii, allows me to spec the header lines, allows me to know reliably what I send, and let's me filter messages and sets of of messages through Unix programs. Let me know when Netscape Messenger is up to these things.