If it is, you won't be able to send or receive emails until you make room.
Check the size limit of your mailbox.
- Email send size limit: 10MB
- Send To limit: 50 contacts per message
- Webmail and SMTP send limit: 35 messages per hour
- Email box storage limit: 700MB
For these domains: centurylink.net, q.com, elpasotel.net, embarqmail.com, centurytel.net, cswnet.com, clds.net, coastalnow.net, cochill.net, emadisonriver.com, emadisonriver.net, gallatinriver.net, grics.net, gulftel.com, madisonriver.biz, mebtel.net, and qwest.net
If you have reached your email box limit, delete messages to free up space for more email.