Mailchimp's tracking links are not getting past many securityfirewalls (including Sky Broadband) and so links simply don't open. We had recent campaigns with up to half of the recipients unable to open links. Mailchimp suggested that people talk to their ISPs. Can you imagine that as a fix. You can't turn link tracking off on free campaigns (even though the control is there and it lets you think you have swicthed it off). Even the paid plans require you keep link tracking on unless Mailchimp are satisfied you have sent enough campaigns which they have approved of. Their answer to the issue - ignore it. We switched to Send in Blue - easier to use and campaign sent like a dream! Bye bye Mailchimp. You have lost the plot!