For anyone who wants to read more, this blog post series goes into quite a lot of detail on ACH (including the FTPing and the fixed-field file format) <a href="http:&#x2F;&#x2F;engineering.zenpayroll.com&#x2F;how-ach-works-a-developer-perspective-part-4&#x2F;" rel="nofollow">http:&#x2F;&#x2F;engineering.zenpayroll.com&#x2F;how-ach-works-a-developer-...</a>