So that was quick; the gmail migration is complete. 18400 emails (and that’s actual count, gmail reports 9400 conversations), a tad under 600mb. It turns out that gmail is quite happy to let OS X mail open a bunch of connections, so all I had to do was make a few temp labels and suddenly I’m copying six lots of 1000 messages instead of one. In fact, it would’ve been done sooner but my modem shut down in the middle of a move last night and OS X mail sat there with the copied mail counters rising far too fast. Needless to say that was quite disturbing.
Half an hour of concerned investigation later it turns out I that not only does gmail merge if you copy an email twice, Mail was actually caching the move. It attempted to complete the process after the internet returned, until I accidentally cancelled it (this was quite surprising, considering I was moving between IMAP accounts).
Oh well, it didn’t waste that much time.
The cool part is that I don’t need to worry about sending via gmail with my normal address. I found the easiest way to set up SMTP on my iPhone was gmail, so I have been using it to send email for a few months now and nobody has been the wiser. All it took was updating gmail to acknowledge I owned my home email address and setting that as the default.
My gmail account has looked a little strange (it had copies of every sent email since July, with none of the received) but it has all worked out in the end.