I'm so sorry to hear your contacts are not receiving your Welcome Email. We have seen cases were some new sign ups through Sign Up Forms (Inline, Pop Up, Wordpress, or Landing Pages) are not getting the default Welcome Email. This is an experience we are continuing to troubleshoot. In the meantime we suggest using an Autoresponder instead. But it is important to note Autoresponders will send to all contacts added to your list, not just those added by a sign-up form.