The following is a list of checks you need to make.
- If your mail is not downloading, check on your mail providers web site that they are not having some sort of outage, or server down issue. After all, whilst things have become quite reliable in recent years, there are no guarantees.
- Next restart Thunderbird with add-ons disabled. (Thunderbird safe mode) Thus us on the help menu (Ctrl + H). If Thunderbird works like normal, there is an Add-on or theme interfering with normal operations, you will need to re enable add-ons one at a time until you locate the offender.
- Restart Windows in Safe mode with Networking. Windows 8 Windows 7 Windows Vista Windows XP OSX If this fixes your ussue, it will be resident software loaded into your computer other than Thunderbird that is the cause. Common problem applications that are not loaded in "safe mode" are anti virus tools, malware detection programs, memory and disk optimisers, privacy protectors and legitimate spy-ware installed by employers to monitor staff. No naming of names here, usually in a home environment it will be anti virus programs, but all security and net nanny type software is suspect.
Finally if you have the urge to say suddenly my mail stopped downloading / working. It is more than likely not an issue with your mail client. Sometimes it is the mail provider changing connection settings so these need to be confirmed. Other times it is following an update to Thunderbird, then it is more than likely the firewall component in your internet security suite / anti virus.