I was on the fence about that. On the one hand it'd keep all that kind of stuff together, which is nice, but on the other hand anyone who implements the interface without extending the Attachment class would have to implement it, even though it's bypassed by half the Mailers. SendGrid and MailGun use raw Curl file attachments or whatever, so if someone implemented a different `getAttachmentContent` that did something other than just `file_get_contents` there wouldn't be any way to use that for those two providers. I ended up doing it this way to make anyone who wants to do something special with the file contents – like generating it dynamically rather than simply loading a file – have to save that to a file themselves before attaching it, to guarantee consistency. Let me know whether you agree!