Original PR description

… seen list

Before, the assumption was made that if email field doesn't exist on the
targeted model, the mail field has to be email_from. So if one model
(for example : account.invoince) is targeted and does not have a field email
nor email_from, get seen list will crash as it's searching at least on email_from
on the targeted model table.

Now, wa apply same 'get email field' rule from
mail_thread.message_get_default_recipients, that gives us all the possibilities
to get the email field of a possible targeted model for sending mails.
Also, since introduction of blacklist and mail.address.mixin,
primary email can be used if defined on the model.

Closes PR #
Task ID : 1907292


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