[imp] Implement Security Code in Compose Page

[Arjen de Korte]

Citeren michel at casa.co.cu:

> I've had problems in my network, since users use very weak passwords  
> and sometimes tend to respond emails where they ask for your  
> password, in order to use their email accounts to bombard servers  
> like Yahoo, Hotmail or Gmail, with messages spam, as spammers  
> putting on black lists.

Have you already set limits on the number of messages users can send  
per hour/day? Typically, when an account is compromised, it will be  
used to send way more messages than you'll find for a normal user  
account. Setting a limit of 100 recipients per hour will be sufficient  
for almost all users. Only those that have a legitimate reason to send  
more messages get higher limits here, but the default is fairly low.

Best regards, Arjen