This plugin is good, thank you. However, I have one problem with it.
It always adds a Reply-To: header, to be the same as the From: header.
However, this is sometimes wrong. For example, I use this plugin - http://wordpress.org/plugins/visual-form-builder/ - as a contact form. it adds a Reply-To: header so that the sender of the contact form can indicate their own address, and I can reply directly to them. Easy SMTP then adds a second Reply-To: header, and then unfortunately my email program uses the one added by Easy SMTP.
Easy SMTP should either not add the Reply-To header at all, or it should check to see if one already has been added.