Hi!
I had the same problem. Than I noticed I was with this other plugin, the SendGrid, activated but without filling the username and password, neither the api key in the configurations. If you have to use their plugin, you have to create a account with them (and be approved) to get an api key. I was using their plugin to send me and to to my costumers emails while they’re buying my products, because I had this problem with my server (it wasnt sending emails, this service was blocked), but i solved it and than stop using the SendGrid plugin.
