This article explains the settings available in the Advanced panel of the Thunderbird OptionsPreferences window. These are settings that aren't used often, such as proxy settings or various advanced settings that only some people need.

General tab

Return Receipts

A return receipt adds a request with your message to notify you when the recipient has opened the message.

Return Receipts Dialog

• When sending messages, always request a return receipt: Check mark this setting to make Thunderbird automatically request a return receipt on every message you send.

When receipt arrives:

• Leave it in my Inbox: Return receipts arrive through email. Select this optionpreference to leave return receipts in your Inbox email folder.
• Move it to my "Sent" folder: Select this optionpreference to make Thunderbird automatically move return receipts to your "Sent" email folder.

When I receive a request for a return receipt:

• Never send a return receipt: If someone sends you a message that contains a request for a return receipt, select this optionpreference to make Thunderbird always ignore the request.
• Allow return receipts for some messages: For each of these cases, you can set Thunderbird to always send a receipt, ignore the request, or choose Ask me, which will make Thunderbird display a prompt when you open the message.

Scrolling

• Use autoscrolling: Autoscrolling is a useful feature which allows you to scroll by clicking the middle mouse button (usually the scroll wheel) and moving the mouse up or down. Some people find this annoying, so autoscrolling can be disabled with this optionpreference.

• Use smooth scrolling: Smooth scrolling can be very useful if you read a lot of long messages. Normally, when you press Page Down, the view jumps directly down one page. With smooth scrolling, it slides down smoothly, so you can see how much it scrolls. This makes it easier to resume reading from where you were before.

System Integration

• Always check to see if Thunderbird is the default mail client on startup: Select this setting if you want Thunderbird to check whether it is the default mail client at startup. Making Thunderbird your default mail client will ensure Thunderbird is used whenever an application has the option to send mail. For more information, see Make Thunderbird the Default Mail Client.

Advanced Configuration

• Enable Global Search and Indexer: This enables Thunderbird's built-in search feature, which allows you to search among all messages you have in Thunderbird. For more information, see Global Search.
• Message Store Type for new accounts: By default, Thunderbird stores mail folders locally in single files (For example, there's a file called Inbox). You can make new accounts store each message in its own file. For more information, see Maildir in Thunderbird.
• Use hardware acceleration when available: Thunderbird can use your computer's graphics processor to display some messages with video and animation. This makes Thunderbird faster since your computer's graphics processor is much better than your computer's main processor at displaying these types of things. This box is checked by default but the feature isn't available for all graphics processors. Thunderbird will enable it when possible.
  If you change this setting you must restart Thunderbird.
• Config Editor: The Config Editor lists all optionspreferences that Thunderbird has loaded. Many of them are advanced optionspreferences, that are not available in the OptionsPreferences window or Account Settings window. In the Config Editor, you can view, edit, and reset those optionspreferences. For more information, see Config Editor.

Data Choices tab

Telemetry

• Enable Telemetry: Enabling this setting will send anonymous data (learn more) to Mozilla about the real world performance of Thunderbird. This information will be used to make Thunderbird better.

Crash Reporter

• Enable Crash Reporter: If Thunderbird crashes, the Mozilla Crash Reporter will appear, asking you if you want to report the crash to Mozilla. With this box check marked, the Tell Mozilla about this crash so they can fix it check box in the crash reporter will default to being check marked.

Network & Disk Space tab

Connection

Your organization or Internet service provider may offer or require you to use a proxy. A proxy acts as an intermediary between your computer and the Internet. It intercepts all requests to the Internet to see if it can fulfill the request using its cache. Proxies are used to improve performance, filter requests, and hide your computer from the Internet to improve security. Proxies are often part of corporate firewalls.

Connection Settings Dialog

• No proxy: Choose this if you don't want to use a proxy.
• Auto-detect proxy settings for this network: Choose this if you want Thunderbird to automatically detect the proxy settings for your network.
• Use system proxy settings: Choose this if you want to use the proxy settings configured for your operating system. (default setting)
• Manual proxy configuration: Choose this if you have a list of one or more proxy servers. Ask your system administrator for the configuration information. Each proxy requires a hostname and a port number.
  • If the same proxy name and port number are used for all protocols, check Use this proxy server for all protocols.
  • No Proxy For: List of hostnames or IP addresses that will not be proxied.
• Automatic proxy configuration URL: Choose this if you have a proxy configuration (.pac) file. Enter the URL and click OK to save changes and load the proxy configuration.
  • Reload: The reload button will load the currently available proxy configuration.

Offline

These settings control how Thunderbird behaves when your computer is not connected to the internet. For example, Thunderbird will not check for new messages, or try to download messages when you select them. When composing a message, the Send button will become "Send Later" and Thunderbird will put your outgoing message in the Outbox, instead of trying to send it.

Offline Settings Dialog

• Automatically follow detected online state: Thunderbird will check if your computer is not connected to the internet. If it is not connected, Thunderbird will switch to offline mode. When a connection is detected, Thunderbird will switch to online mode.
• Manual state when starting up: If Automatically follow detected online state is not enabled, this will determine how Thunderbird decides if it should be in offline mode when you start it. Setting this to Offline will make Thunderbird always start in offline mode. Setting this to Online will make Thunderbird always start in online mode. Ask me for online state will make Thunderbird always prompt you which mode to choose. Remember previous online state will make Thunderbird open in the mode it was set at when you last closed it.
• Send unsent messages when going online: If you have any messages in your Outbox, setting this to Yes will make Thunderbird automatically send those messages when you switch to online mode. When set to No, messages in your Outbox will not be sent. Setting this to Ask me will make Thunderbird prompt you to send messages in your Outbox when you switch to online mode.
• Download messages for offline use when going offline: If you have any offline folders set to keep a copy of every message on your computer, setting this to Yes will make Thunderbird automatically download any messages in those folders you don't have stored locally when you switch to offline mode. When set to No, local copies of messages will not be synced. Setting this to Ask me will make Thunderbird prompt you to download new messages from online folders when you switch to offline mode.

Disk space

Messages you view, which are not kept on your computer, are normally stored in a special cache folder for quicker viewing the next time you view the message. You can specify the amount of disk space the cache can use here. You can also immediately clear the contents of the cache.

• Clear Now: Immediately clears the current contents of the cache, freeing the disk space used by the cache.
• Use up to ___MB of space for the cache: This box allows you to specify the maximum size, in megabytes, of the cache on your computer.
• Compact all folders when it will save over ___MB in total: When a message is deleted, Thunderbird will keep it stored, and mark it as deleted so you won't see it. Compacting a folder removes any messages from storage that have been marked as deleted. This will make message lists load faster, and take up less disk space. Checking this box allows you to specify the maximum size, in megabytes, of the folder before Thunderbird will automatically compact it.

Update tab

Certificates tab

Certificates help perform encryption and decryption of connections to websites.

• When a server requests my personal certificate: Some servers ask you to identify yourself with a personal certificate. In order to do so, they ask Thunderbird to generate one for you. When you access a server in the future, Thunderbird will ask you for which certificate to use. If you wish to have Thunderbird automatically choose a certificate for you, select the Select one automatically optionpreference.
  Note: A personal certificate can contain personally identifiable information, such as your name or address. It may therefore harm your privacy if you select the Select one automatically optionpreference. If you do, you will not be alerted when a website request your personal certificate, and you may lose the ability to control who can access your personal information.

• Query OCSP responder servers to confirm the current validity of certificates: Thunderbird may ask an OCSP (Online Certificate Status Protocol) server to confirm that a certificate is still valid. By default, Thunderbird validates a certificate if the certificate provides an OCSP server. You will most likely only need to change this if your Internet environment requires it.

• Manage Certificates: Click this button to view stored certificates, import new certificates, and back up or delete old certificates in Thunderbird.

• Security Devices: Security devices can encrypt and decrypt connections and store certificates and passwords. If you need to use a security device other than the one in Thunderbird, click the Security Devices button.