I don't really consider this a bug in mojoPortal, seems like a bug in outlook and I don't really want to try using less than the full guid or shorten the url or use any 3rd party url shortener.
I have 2 suggestions to try, first is go ahead and add the brackets and see if that works. Just edit the file
let me know if that solves it and I'll make the same change.
The other suggestion is get the latest source code, deploy a new build and add this setting in user.config:
<add key="NewsletterUseHtmlEmailConfirmation" value="true" />
I just now implemented support for this setting and pushed it to the repository. By using an html email instead of plain text the length of the url should not be a problem. The default setting is false. The new html template is:
Hope that helps,