I use gmail and it never got full I have used only 5% of my total available space so far. Gmail is BEST
im not sure which inbox are you questioning for, but for inbox in this forum i already more than third time been warning since im quite lazy to delete some old PM.
A few years ago, yes. Now, with providers offering storage in GB terms, I think that that having your e-mail inbox full is a matter of the past.
If you are talking about DP inbox then never because will take backup when it reach 850 to 900 and then remove old PM's. If you are talking about mail inbox then yahoo and gmail provide lot of spaces free so no more worries there
If talking about DP then i had around 96% full yesterday but deleted some, down to around 800pm's stored now. Gmail, no worries.
About 5 times. I have 5-6 PM .csv backups on my hard-drive(just in case ) Got another 100+ PMs today and sent 150+ ... time to delete all again