All mailboxes are limited in size, and your size limit depends on which mail service you are using. If your inbox has reached its quota, you will receive continuous emails stating this and you may stop receiving emails, so urgent action is advised.
Firstly, try deleting emails (emptying spam, sent items and deleted items folders is a good start). The best place to do this is through your online webmail platform, to ensure that emails are deleted from the server instead of just your device. To access online webmail, please see this article.
We can also usually offer larger mailboxes, which are a great option if you are a particularly heavy email user.
If you're still having problems, or want to look at expanding your mailbox, please call customer service on 0330-122-1010 (UK) / 844-411-0200 (North America) or email firstname.lastname@example.org for more information.