I actually have my @gmail.com address redirect to Fastmail, I have a filter on the Fastmail inbox that shows me mail sent to the gmail address.

I go through the filter every now and then to see which services are still using my old address and change them to use the newer one.

It's also a nice way to find out how horribly some services have f-d up the change process. One had a non-working change email button and the CS rep just deleted my old account and told me to create a new one.

One just plain doesn't let people change their email. At all.

Combined with regular backups (maybe to an offline client, using IMAP?), sounds like a good idea to me.

Actually, I've been thinking about doing the same thing.

But i don't know much about emails.