Most web analytics tools rely on javascript:document.referrer to get the ‘referrer’ for a page, or the page you were at just before you came to this one. Analysts will use this to see if a particular site is driving a lot of traffic via a link or an ad. The explosion of webmail clients means you can also tell when people are coming from an email. You’ll have a referrer from webmail.aol.com or mail.yahoo.com , etc. While best practices dictate that you don’t rely on referrers as your sole determinate of email success, you might try to classify your traffic into email, websites, search engines, and bookmarks, based on your referrals. Unfortunately, gmail causes some issues.
If I use Yahoo mail and click on a link, then paste javascript:document.referrer into the browser window, I see the yahoo address. If I use gmail and do the same, because the link opens in a new window, the referrer is null. If I use gmail but specifically open the link in another tab, the referrer is gmail.
If the users are more likely to click on the link and not open it in a new tab, then your Direct/bookmarked referrals will be overinflated and your email traffic too low because of the gmail loss. You should compare your referrals with your actual email metrics (you should be coding your email links with some parameter to track the clicks) to see what percent you might be losing. You’ll get a more accurate picture of your traffic sources.