Customize Your Server Settings – Set Up Priorities
Once you have all your email addresses set up, you can go a step further in prioritizing how Thunderbird handles all your email accounts.
There are some emails that don’t need to be checked the moment you fire up Thunderbird, some that don’t need to be checked every 10 minutes, and some that don’t need to be checked until you say so.
Make sure to go through each individual account and set them up to do what you want them to — this will pay off in the long run (trust me).