function verifSelection() {

    if (document.mail_form.champ1.value == "") {
        alert("You must enter the name of your company.")
        return false
    } 

    if (document.mail_form.champ2.value == "") {
        alert("You must enter a contact name.")
        return false
    } 

    if (document.mail_form.zone_email1.value == "") {
        alert("Please fill a valid email address.")
        return false
    }

    invalidChars = " /:,;'"

    for (i=0; i < invalidChars.length; i++) {	// does it contain any invalid characters?
        badChar = invalidChars.charAt(i)
        
        if (document.mail_form.zone_email1.value.indexOf(badChar,0) > -1) {
            alert("Your e-mail contains invalid characters. Please check.")
            document.mail_form.zone_email1.focus()
            return false
        }
    }

    atPos = document.mail_form.zone_email1.value.indexOf("@",1)			// there must be one "@" symbol
    if (atPos == -1) {
        alert('Your e-mail does not contain the "@". Please check.')
        document.mail_form.zone_email1.focus()
        return false
    }

    if (document.mail_form.zone_email1.value.indexOf("@",atPos+1) != -1) {	// and only one "@" symbol
        alert('There must be only one sign "@". Please check.')
        document.mail_form.zone_email1.focus()
        return false
    }

    periodPos = document.mail_form.zone_email1.value.indexOf(".",atPos)

    if (periodPos == -1) {					// and at least one "." after the "@"
        alert('You have forgotten the point "." after the "@". Please check.')
        document.mail_form.zone_email1.focus()
        return false
    }

    if (periodPos+3 > document.mail_form.zone_email1.value.length)	{		// must be at least 2 characters after the 
        alert('There must be at least two characters after the sign ".". Please check.')
        document.mail_form.zone_email1.focus()
        return false
    }

}