I installed EXM 3.0 and used the instruction about upgrading from ECM 2.2 to EXM 3.0. (Sitecore ECM: Can't access Email Campaign Manager). After installation, I clicked "Email Campaign Manager" from Sitecore start menu and it goes to "Page not found" page in the url "mysite.com/speak/emailcampaign".
Did I miss something?
I installed this module in our testing server which has both CM and CD in the same location. So, I enabled "Sitecore.EmailCampaign.Xtune.CD.config".
If you've installed EXM properly, you won't be able to access it at the URL you've specified (mysite.com/speak/emailcampaign). Instead, it will appear as an app in the Launchpad: mysite.com/sitecore/client/Applications/Launchpad.
In any case, as Anton suggested in his answer to your previous question, it will be much better if you start over. Right now, your Sitecore is likely broken (to a degree) due to the incompatible versions of both SPEAK and ECM that you've installed. You'll be better off by setting up a clean instance of Sitecore 8 and then installing EXM.