{!-- Set defaults --}
{exp:stash:recipients}{/exp:stash:recipients}
{exp:stash:user_recipients}no{/exp:stash:user_recipients}

{!-- Set Stash variables for email contact form --}
{exp:stash:set parse_conditionals="yes" parse_tags="yes"}
    {exp:channel:entries
        channel="advertisers"
        disable="categories|category_fields|pagination"
        entry_id="{embed:advertisers_entry_id}"
    }
        {if {absolute_results} == 1}
            {stash:recipients}{if "{advertiser_email}"}{advertiser_email}{if:else}{author}{/if}{/stash:recipients}
        {if:else}
            {stash:user_recipients}yes{/stash:user_recipients}
        {/if}
    {/exp:channel:entries}
{/exp:stash:set}

{!-- Use Stash variables in email contact form --}
{exp:email:contact_form
    charset="utf-8"
    form_class="customer-email-form"
    recipients="{exp:stash:recipients}"
    user_recipients="{stash:user_recipients}"
}
{/exp:email:contact_form}