While doing an install or migration of Exchange to a new server one of the things I often need to do is configure all the mailbox databases at once to unlimited.
Now this is something you can certainly in the GUI but if you have more than 1 database to change then the GUI gets old fast.
You can do this easily in the Exchange Management Shell.

First you might want to record the current settings. I would run this Command to view the current settings:
*in each of these examples change SERVERNAME to the name of your server.

Get-MailboxDatabase -Server SERVERNAME | FL name,issuewarningquota,prohibitsendquota,prohibitsendrecievequota

To set the Issue Warning Quota:

Get-MailboxDatabase -Server SERVERNAME | Set-MailboxDatabase -IssueWarningQuota unlimited

To Set the Prohibit Send Quota:

Get-MailboxDatabase -Server SERVERNAME | Set-MailboxDatabase -ProhibitSendQuota unlimited

To Set the Prohibit Send / Receive Quota:

Get-MailboxDatabase -Server SERVERNAME | Set-MailboxDatabase -ProhibitSendReceiveQuota unlimited

IF you want to set all at the same time:

Get-MailboxDatabase -Server SERVERNAME | Set-MailboxDatabase -IssueWarningQuota unlimited  -ProhibitSendReceiveQuota unlimited -ProhibitSendQuota unlimited