If you are unable to send/receive email, the first question is - how are you trying to send email? Is it via Microsoft Outlook or a similar mail client such as Mozilla Thunderbird?
The typical customer sets up multiple email accounts on mail clients on multiple devices using a shared internet connection. The problem arises when an incorrect account is added, i.e. a wrong email address or username, or the wrong password. Email clients are configured to auto-poll for new email, and if the wrong details have been setup, our server will see multiple invalid login attempts and eventually ban your IP thinking you may be a hacker.
If you can successfully send/receive email then your location's IP is most then likely blocked by the server firewall.
In this case, please open a support ticket providing your location's IP address. If you do not know what your IP is, or if your ISP assigns you dynamic IPs, then please visit the website http://www.whatsmyip.info from an affected device using the affected internet connection and your IP will then be displayed.
Once we have your IP we can check if it is blocked and then unblock it for you.
Please note that we do not whitelist customer IPs on shared hosting servers.
If your IP is not blocked and you are unable to send email via Webmail, please then provide us with an email address and password so we can replicate the error as this will help us track down the root cause and fix it.