Regarding the second assumption that free webmail is less responsive than pay-for email accounts, we follow this sort of thing fairly closely, and I can say that users at webmail are easily as likely to click on a message that they have opened than users at pay-for ISPs.

Gmail exhibits the highest click to open rate (much higher than at pay-for ISPs) while Hotmail is slightly higher than pay-for ISPs and Yahoo is about equal.

The trick here is that not as many of these recipients are likely to actually open a message, perhaps because there are more junk email addresses in the mix, but more likely because these places tend to have more aggressive spamfiltering in place and fewer messages are being delivered to the inbox. Thus, relevancy is (as usual) key.

If your message is relevant, desired and expected then you will have good response rates at free webmail providers… especially so at Gmail.

At least, that’s my experience pouring over about half a billion sends (for what it’s worth ).