Can we use a sender that is a GMAIL account ?
No this is one of the significant changes – The major ISP / Webmail providers have an alliance where for the purpose of preventing SPAM Yahoo, AOL, Gmail Hotmail etc will bounce any email that has not from the known source which is shared between therm. The only exception is if you have a domain like zululabs.com and gmail is your corporate mail server. Then we need to add some authentication. All mail originates from us anyway unless you are an enterprise customer.