More than you think, but not as quickly as you expect.

Annnnnddd we’re back to the most common answer on Ask Leo!: it depends.
It depends on the email service, of course.
But it also depends on your behavior after you indicate you close the account.
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Closing an email account
Closing an email account starts a countdown. At first, nothing happens. After a while, all your emails, contacts, and other info are deleted. You may lose access to other services, too. Later, someone else might get your old email address. My advice: don’t close it, just in case.
1. A grace period
In most cases, when you close an email account, the account is not closed right away.
What actually happens is… nothing. Typically, that’s quite literal: nothing changes at all. Your account continues to receive email, and everything in your account remains in your account.
The only thing that really happened is that a timer has started. This timer, or grace period, allows you to change your mind. If you do anything with the account at all, the account closure is canceled. The assumption is that by using the account, you’re saying you don’t want to close it.
The length of the grace period varies from service to service. In some cases, it’s zero days; in others, it can be several months.
Unfortunately, “doing anything with the account” can be quite literal. For example, if your email account is with a company like Google or Microsoft, which provides other online services, then using those services may be taken as an indication that you want to keep the account. And you probably do, since closing the email account would cancel all the other services associated with it. For example, do you want to lose the YouTube account associated with that Gmail account you just closed?
Be certain that you really want to close everything associated with the account before you do anything.
2. Housecleaning
After that grace period, which varies from provider to provider, all content associated with the account is deleted.
This includes all email and all your contacts.
It also includes any other data associated with the service, such as calendars, online storage, photos, or whatever other services that are associated with this account.
Once deleted, this data cannot be recovered. You may still be able to sign in to the account and cancel its deletion, but everything within it is gone forever.
If the service sends bounce messages because the account no longer exists (which it may or may not), that function likely starts now.
3. Difficulty signing in
Particularly if you’ve had the account for any length of time, you’ve probably used the email address at a plethora of online accounts, either as a primary identifier or login ID, or as a backup “alternate” email address.
Those stop working. Eventually, services like banking, shopping, and social media that still use your old email for sign-in or password recovery will lock you out.
Make certain you change your username everywhere before closing your account.
4. True death
After that grace period, which varies from provider to provider, the account is completely deleted and is no longer recoverable.
You cannot sign in. Email sent to it will probably bounce.
The account is well and truly closed.
5. Resurrection
This is a step many people overlook. At some point (which, again, varies), the email address associated with your account may be made available for re-use.
Let’s say your email address was joey@randomisp.com. You closed it, and all the steps above took place. If someone else creates a new account with that same service, they could choose your old address: joey@randomisp.com.
None of your old data would be present (it was deleted in step 2), but any new email sent to your old email address would now go to them. Any account you failed to update with your new email address risks being accessible to the new owner of your old email address. While you might not think they’d know which accounts to try, if a malicious individual was the new owner of your old email address, they could try using it at lots and lots of different popular services. That’s exactly what hackers do, and there’s a high likelihood you’ll have an account one or more.
Not all services allow email address re-use, but even if they don’t today, I expect most will eventually.
Do this
My advice? Don’t.
Seriously, don’t close the account. Ignore it, if you like, other than signing in every so often to keep it alive. This does two things:
- It preserves anything you didn’t realize would be lost should the account close for real.
- It keeps the email address in your control, not someone else’s.
That last point, to me, is perhaps the most important.
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