When I click that link at the bottom of my gmail screen where it says "Last account activity: 0 minutes ago at IP 220.127.116.11 Details". I click the link and sure enough, it shows accesses from my own IP (IMAP and browser), but it also shows IMAP access from this IP 18.104.22.168, which appears to belong to an Amazon EC2 instance. I can't think of any reason why an EC2 instance would be accessing my email. Should I be concerned?
Update: I changed my password an hour ago and logged back in from my browser and my iPhone, and then went out to dinner. Now it's showing accesses from my home IP (browser and IMAP), and IMAP accesses from 22.214.171.124 (Amazon EC2), 126.96.36.199 ("Service Provider Corporation"), and 188.8.131.52 (AT&T). So either AT&T or Apple is using 184.108.40.206, or some other app on my iPhone got my gmail password and is sharing it with people they shouldn't.