As the issue is impacting a number of people there's a team working on the problem. Which email domain are you using (e.g. tiscali / lineone / another) and is it just webmail not email sent from a client like Outlook or Thunderbird or a gMail app, for example?
Service status is reporting a fault and there will be updates:
"We're aware of some customers having issues when they try sending, replying or forwarding emails. Our engineers are looking into this as a priority, and looking into fixing as soon as possible. We apologise for any inconvenience caused."