If you find yourself unable to send messages from the Gmail app after restoring a Nandroid backup (outbox emails perpetually say "sending..."), and you might also notice that emails you mark as read still show up as unread on your desktop Gmail, then you need to do this:
Settings: applications: manage applications
Wait for list to load...
Find "Gmail" and clear its data
Find "Gmail Storage" and clear its data
Reopen the Gmail app and wait for it to sync
You should be able to send Gmail again after that. Note that any unsent emails (the ones that said "sending...") will be permanently lost after you do this, so you'll need to recompose them.
Settings: applications: manage applications
Wait for list to load...
Find "Gmail" and clear its data
Find "Gmail Storage" and clear its data
Reopen the Gmail app and wait for it to sync
You should be able to send Gmail again after that. Note that any unsent emails (the ones that said "sending...") will be permanently lost after you do this, so you'll need to recompose them.