Mozillas Thunderbird

Useful extensions:
There are lots of extensions available, but only some should be installed, 'cause a huge amount of extensions installed, will slow down the overall performance.
This is the list of extensions, I really recommend to have:
  • Addressbooks Synchronizer
    Synchronizes selected addressbooks
    • with local files (resp. files on network shares)
    • with files via FTP or WebDAV (http or https)
    • with files stored in an IMAP folder
  • Lightning
    An integrated calendar for Thunderbird.
  • MoreColsForAddressBook
    Adds to the address book more features, like the possibility to edit some properties in multiple contacts with just one action, adds an extra tab with the birthday date, the spouse name etc.
    It can be used in conjunction with ThunderBirthDay (see below).
  • MR Tech Local Install
    The primary goal of this extension is to provide the tools needed to install and manage extensions and themes locally.
    (Note: This extension can be used also in Firefox.)
  • NotTo
    Enables you to avoid sending mail to specific recipients when you use mailing list containing a lot of recipients and you wish to avoid sending the mail to specific individuals.
  • Quote Colors
    Configure text and background colours for different quote levels in mail/news messages.
  • Signature Switch
    Switch the signature on/off or choose a new one from your predefined set.
    Additional features include the support of fortune-cookie-files and automatic switching based on recipients.
  • ThunderBirthDay
    Display birthdays from the Thunderbird address books as events in Lightning.
    Needs the MoreColsForAddressBook extension as well.
  • WebMail
    This extension integrates web site based email accounts (like Hotmail, Yahoo, AOL, ...), which allows Thunderbird to download and to send emails using the web site.
Note: On Ubuntu you shouldn't install any extension directly from your applications menu, but from the .xpi, otherwise Thunderbird can't update them automatically anymore.

Related software:
You might like to use Mail Notification for receiving advises about new mail arrivals in your mail accounts.