builder.go
func (p MailBuilder) From(name, addr string) MailBuilder {
	p.from = mail.Address{Name: name, Address: addr}
	return p
}
func (p MailBuilder) From(name, addr string) MailBuilder {
	p.from = mail.Address{Name: name, Address: addr}
	return p
}
// From returns a copy of MailBuilder with the specified From header.