We've just finished compiling our largest ever study of email client market share. We've tracked data across 250 million email recipients, and can now reveal the most popular email clients in use today. Here's the top 5.
It's no surprise that Outlook continues to dominate the email client landscape. However, it's somewhat reassuring to know that Outlook 2007 is still only being used by around 1 in 10 recipients.
Hotmail and Yahoo! Mail are (slowly) losing ground, whilst Gmail gradually gains popularity. Impressively, iPhone ranks as the 6th most popular client.
You'll probably want to read the full report. It includes hard data for the top 10 most popular email clients, and some background on how we carried out the study.
I hope these statistics will help guide you as to what email clients you should be testing against. However, remember that the email client market share for your own mailing list may differ significantly from these averages. I'd recommend analyzing your own list to have the more accurate data.