What we have hyar is a failure to Communcate

You could start here ::
http://boards.cityofheroes.com/showthread.php?t=122411

With Zombie Man's Guide to Guides
in the Player Help section > Player Guides

There really isn't anything concrete down about ethics of e-mails, tells, joining teams, or sending team invites other than what is in the EULA and Rules of Conduct.
I'm assuming you mean teaming by "team" and not supergroup invites.

There is an option for setting preferences on your e-mail status in the Options menu. I suggest using it to limit who can send you e-mails and it will stop the RMT'rs (aka Gold-farmer) e-mails. These e-mails are against the rules and there is a button to report them as spam.
You shouldn't be e-mailing anyone you don't know (as far as I'm concerned).

If you don't want to get tells from someone, the use the /ignore [character name] or /gignore [character name or @global name].
Generally, the people playing this game are pretty cool about getting tells. If you ran into a jerk that's giving you attitude because you sent them a tell, they are few and far between. Some might let you know why it was a bad idea to send them a tell.

If someone's name is Red in the search window, don't bother them. The Red means that the "aren't looking for anything".

Be polite, don't blind invite. Blind inviting is when you get a team/sg invite out of the blue. You have no idea who the person is.
Be polite.
Send a tell with a message asking if someone would like to join a team before sending an invite. In fact, wait for them to say that they want to join before you send an invite - unless you get the message that they are on a trial and then just send an invite and they will take it or not.
I suggest including the level of the missions you will be running and the kind of missions you plan on running.

When using the search window, you are primarily looking for players names that are in "sky blue". They aren't on teams.
Also on the far right hand side, there are notes about players current statuses. Check this before sending a tell asking them to join a team.

Players that are in purple are team leaders. Don't send chat to "team leaders" blindly by using players that are showing being on teams. This could very well send a bunch of tells to the same team leader who may decide you are a spammer - report you as a spammer, or just put you on ignore.
If the team leader is in your level ranger or lower, you are more likely to get an invite then if you send a tell to someone of a much higher level. When you sent that the tell, make sure to send your level and your archetype.

If someone replies to your tell and says they can't help with whatever, I think it's polite to thank them for taking the time to reply.

That's pretty much the basics.