The address book is not the best place to start an email.

Open a Write window and press F9 to turn the contact sidebar on and start from there.

I cannot explain what is happening in your case but I never start there and this is the reason. It works better from a Write window

(Thunderbird 31.5.0) Although I use that method, the outcome is the same: if there are more e-mail addresses for the contact, the address comes out with too much punctuation. Try it: add an address to some contact, and then pick that one.

Have you sanitized your address books following the import from Eudora? You were still going on this topic https://support.mozilla.org/en-US/questions/1051728 earlier this morning which indicates your address book contains all kinds of interesting things. Export your address book to a spreadsheet and edit out the rubbish and re-import before you do anything else.

(Thunderbird 31.5.0) Although I use that method, the outcome is the same: if there are more e-mail addresses for the contact, the address comes out with too much punctuation.

I added a secondary email address, I clicked on it in the address book I clicked on Melinda and a compose window opened with the secondary address shown in the To field.

(Aside from this I rather keep "Display Name" empty because I do not want my messages automatically decorated.)

If you do not want Thunderbird using display names from your address book, turn the option off instead of mucking around in the address book. Tools > options > advanced > reading and display.

You seem to be like many Ex Eudora users fighting to continue to do it the Eudora way. Unfortunately the Eudora way of most things was unique and usually incompatible with other mail programs.

The quoted question was about address entries in imported messages, not about the address book. There is no resolution for that one (then what do I do?). My address-book question was https://support.mozilla.org/en-US/questions/1051685 . I already unchecked the option "Show only display name for people in my address book", since I want to see the actual e-mail address in incoming e-mail. I added a Contact with Display Name "joak" and Email "agent99@control.org,agent86@control.org". When I pick it for an outgoing message, at first it yields joak <""agent99\"@control.org,agent86@control.org"> , which has too much punctuation. If I highlight that and right afterwards something else, it splits in twain: joak <"\"\"agent99\""@control.org> agent86@control.org"> —and both these are also wrong. If there is no Display Name, it simply becomes twain correct entries. It further seems to me that Thunderbird cannot decide whether it supports more e-mail addresses in Contact field Email or only one, and that is a problem. Of course, I want it to support more. There is an outstanding bug report (943821), a feature request, for selective use of Display Name, something beyond a global switch. From this it is clear that the design feature, using Display Name for the key whereby one finds one s Contacts, is a bad idea. There are more reasons for that: say one has correspondents John Smith and John Smith: the only reason for not giving them the same Display Name is that it is also the key. Furthermore, if one has an Contact for John Smith at work and John Smith at play, the same applys, not to mention that for close family the natural key is, maybe, a nursery word (along the lines of "twee" for "sweet") not for use outside the family. (In Eudora they were distinct, and that indeed was better.)

You will also find a bug to officially support comma delimiter mail addressing, just because it works does not make it supported. One address per line is how Thunderbird officially does it.

I added a Contact with Display Name "joak" and Email "agent99@control.org,agent86@control.org".

Well, at least that answers one of my questions. (But it does not excuse Thunderbird from making a bad situation worse.) Really, I want more addresses in a Contact because I use the Address Book for filtering, filtering the many commercial messages to which we signed up. I wish that if not Email then Additional Email allowed more e-mail addresses at which the filter looked. Then I would be spared adding a duplicate Contact (no Display Name needed, I never send those any messages) for every e-mail address the company uses.

There is the next problem. Message Filters make appalling spam filters. They are ok to block a domain or an ex, but they are not intended for the use your putting them, hence in time you will have filter problems.

There is a Bayesian spam filer in Thunderbird, unless you train it by setting mails as ham or spam it is basically useless. Filters unless the start by marking as spam defeat that completely. so you end up on a merry go round of spending more time on filters than it would take to read and manually delete the spam.

There is a good discussion on spam filtering here http://kb.mozillazine.org/Junk_Mail_Controls including suggestion on add-ons and third party spam management tools.

oldProgrammer said

... filtering the many ... messages to which we signed up.

Signed up!