Each Google Account has a storage limit or quota. Free Google Accounts usually have a 15GB storage limit. Other plans have other storage limits.
The storage space used by all of your Gmail messages, Google Drive files, and Google Photos is all combined and must fit within the storage limit of your Google Account.
Over Quota
When your account is near its storage limit, you might see a warning. Once you reach or pass your storage limit, you will stop receiving emails and won't be able to create or upload additional content into your Gmail, Drive or Photo areas.
You have two options: reduce your storage usage or increase your storage limit by paying a fee to Google.
Reduce Your Storage Usage
In general, here are some examples of how to reduce your storage usage:
- Delete unneeded gmail messages from your inbox or other folders.
- Delete unneeded gmail messages from your Sent area.
- Delete unneeded files from your Google Drive and Google Photo areas.
- After all of your deletes are done, then clear out the Deleted Items folder.
In addition, you might want to delete gmail messages which contain large attachments. You can search for large gmail messages entering the following search command into the gmail search box:
has:attachment larger:5M
The above command will search for all gmail messages which have at least one attachment and which are also consuming more than 5MB in storage for their message content plus attachments.
You might also want to delete gmail messages which are older than a specific date in the past, i.e. that are a few years old. For example, to search for all gmail messages which have a date before Jan 1, 2017, enter the following search commend into the gmail search box:
before:2017-01-01
You can even combine those two search commands to, for example, search for all gmail messages from before 2017 which have attachments and which consume more than 5MB of storage each:
before:2017-01-01 has:attachment larger:5M
Each of the above search command examples will generate a list of gmail messages which match the requested criteria (if any). You then need to review the list of gmail messages and delete the messages which you no longer need to keep.
After all of the deleting is done, make sure that you clear out the Deleted Items (Trash) folder to actually purge/remove the deleted items from your account.
Increase Your Storage Limit
There is usually an [Upgrade] button or link available near the "over quota" message. It's in different locations in different Google areas, but Google is always happy for you to upgrade, so there will be a button or link somewhere, usually near any storage total or over quote / over limit notification. Upgrades will cost you a monthly or annual fee paid to Google.
See this
article for details on increasing a user's storage limit.