Having a custom tracking domain (i.e. clicks.domain.com) would not only look more professional but would also resolve a lot of the current spam issues.

For example, when you currently send out an e-mail that contains copy similar to:

"visit domain.com for more information"

The actual hyperlink for domain.com is changed to app.convertfox.com and therefore marked as spam. (This can be avoided by simply not mentioning the actual domain your copy, but is still not ideal)