If you use our basic email system, you may have noticed a delay when sending email. It appears that your email client has stalled (Mozilla Thunderbird is particularly noticeable), waiting on our servers to respond. This is correct, that is exactly what is happening.
We employ an anti-spam security feature that prevents robot and rouge servers from using our system to spew spam to our users or even hijack your account. This feature imposes a delay on any connection trying to send mail using our system. This delay is not tolerated well by robots and they usually just go away once they encounter the delay.
Think about it this way. Spammers want to send as much mail as is possible in a short amount of time. Since they don't have the courtesy to use their own email servers (which might mean getting caught), they try to use the mail servers that belong to legitimate companies. They do this by using a compromised email account (which is a good reason to have a strong password). Once they have a compromised account, they setup a robot to use that account to start sending their garbage. That's where the delay comes in.
By having our server delay responding to the request to send email, we cause the robots and spammers to go away. They cannot wait for a 10 or 20 second delay to send each email. With thousands of emails t send and thousands of delays, it is not worth their time t sit around and wait.
The beauty of this is that the delay is short enough that legitimate email clients can tolerate the wait. They usually do this in the background, so the end user does not notice. In some cases, like with Thunderbird, the email client does this in the foreground, forcing the user to wait. The good news is that there is almost always a setting that will tell the client to do its processing in the background.
I mentioned Thunderbird, so its only fair to post the fix so Thunderbird will process in the background:
Preferences -> Advanced -> General -> Config Editor and change mailnews.sendInBackground to true and restart Thunderbird.