> when a user clicks "send", the email client has to make some tcp-connection > to some ip address. > what if the hostname configured at the email client resolves to multiple ip > addresses?
There are several hops that could randomize ips: - authoritative dns server - dns resolver at your dialup provider - dns resolver at your home router - dns resolver at your computer Usually there is no need for authoritative dns servers to rotate ips because dns resolvers do. So your email client just gets a list of randomized ips. In my experience the first one is used and if the connect fails it will try the next one. This works at least with Thunderbird, Outlook and Apple Mail. Remember that dns lookups are cached (ttl / time to live), so this particular email client may stick with the same server for some time, but on a global view requests are distributed quite evenly because of resolver behaviour. Over time you will see that your email client uses both mailservers. DNS loadbalancing works very well. Some companies combine that with dedicated loadbalancers to cope with the load or use bgp anycast. Best regards Gerald
