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 (i.e. bounced).
What does this mean for you? It means you can't use your @gmail address as a sender on email marketing services (like Pathway). You will have to use a different email address in the FROM field of the newsletters you send.
What other address can you use? Unfortunately, Yahoo and Microsoft have already done the same with their DMARC policies. This means that you also can't send from an @yahoo, @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.