tcpstat

When you are downloading GMAIL via imaps(ssl) or pop3 protocol as me. It's very useful to looking into the download speed with tcpstat, it can be installed in one command and monitor this way:

sudo apt-get install tcpstat
sudo tcpstat -f 'port imaps' -o '%B\n' 3

Every 3 seconds, the average protocl specific BPS statistics will display on screen (terminated with newlined).