Originally posted by stevebrot No, they queue. The slow parts are in determining the route, the negotiation with the receiving server, network latency and bandwidth (bits/second)*. Latency at each hop along with server negotiation can be considerable such that the time to send even a small message can be upwards of a full second in a non-optimized environment. Bulk e-mail providers typically have hot access to back-bone networks and significant computing power to allow adequate throughput.
Thanks! That's pretty much what I expected and also what seems to be happening as the emails are reaching more people.
I'd think tens of thousands of people (or more!) downloading all their photos en masse will also be a non-trivial thing. IIRC, flickr would dump the full resolution versions of photos that are rarely accessed into less expensive and less quickly accessed storage (they had a blog post with more details that I can't find at the moment). For people using their accounts to backup large photo collections, this might apply to many of their images. I'm also willing to bet that even if they don't plan to abandon the smugmug ship before it's even docked, this announcement has prompted many people to download everything "just in case".
It might be a fun, coffee filled time at flickr right now.