clipped from blog.bronto.com

Do personalized subject lines work? Do they lead to more opens/renders, higher click-through rates, a bump in conversions?

Answer: It Depends!

Ask yourself, is personalization relevant to your audience?

What is your goal with your personalization tests? Higher open/render rates? More click-throughs? An increase in conversions? This is critical. Some tests will prove that personalization will lead to higher opens, but if there is no noticeable positive impact on conversions (and this matters to your program), then who cares?

Your subscribers may not respond the same way if you personalize on every single email. Mix it up once in awhile.

Bad data can cause incorrect (”Dear Firstname,” or “Dear Bob,” when their name is Mary) or even blank (”Dear  ,”) content, potentially endangering the trust and credibility you have built with your recipients.

Any way you slice it, it all boils down to testing.