To make sure you write emails following the guidelines, read the Netiquette Guidelines - RFC 1855.
Or play this game of goose (in French): Quelques règles pour les emails
This can be done with several email clients (MUA = mail user agent).
I used the following at some point:
I have installed LDAP on my server and tried a few email clients and address books:
The biggest problem is that the mail clients and address books don't use the same schemas.
They only items they have in common (that I am interested in) are: