SENDING EMAIL FROM FILEMAKER has improved with recent versions but still leaves much to be desired. There are solutions out there from different vendors and developers, but most require a plugin and still rely on FileMaker client or server to do the heavy lifting of sending the email (and attachment).
This solution from Daniel Wood of Digital Fusion is pretty nice, and it appears to work without a plugin. Feedback from the FileMaker community (via comments) has resulted in a stronger solution, but it appears to be evolving still. This solution, among other things, allows a developer to offload the email process to an outside service yet still appear to be the sender:
You can use Mandrill to send Email via standard SMTP, or via their API. Even if you wish to use it just via SMTP alone it makes sense. The Mandrill SMTP credentials are reliable, secure, and work anywhere (subject to firewall restrictions of course). In addition, you get all the benefits of comprehensive email tracking and settings to help customize the experience.
In this article we will be covering sending Email via Mandrill by using their API. The benefit of this method is the Emails are sent using an HTTP POST request on port 80 so unless you work for a totalitarian company which has blocked the internets then you should be guaranteed that your Emails will send every time.
Study (don’t just read) the whole thing.