Recently Gmail made a change to their DMARC policy. This means that they're telling other servers that any email with a @gmail FROM address, not sent through Gmail, has to be refused(ie. bounced).
What does this mean for you? It means you can't use your @gmail address as a sender on email marketing services(like us). You will have to use a different email address in the FROM field of the newsletters you send.
What other address can I use? Unfortunately, Yahoo and Microsoft have already done the same with their DMARC policies. This means that you also can't send with a @yahoo nor a @hotmail, @aol or @outlook address. The best solution is to use your own domain.
If you don't have an alternative email address to use, consider buying yourself a domain and private email hosting.