Note: There are a few cases of duplicates in user autocompletion which are being worked on.

MailNews Core
Mail and news components common to Thunderbird and SeaMonkey
Select a component to see open bugs in that component:
Problems with setting up accounts within MailNews.
Problems with the address book backend and shared frontend bits
For problems with mail or news message attachments.
Problems with RDF data sources and application logic. Most likely, your problem can fit in one of the other components so this component should be rarely used.
Bugs concerning the comm-central build system and build problems with that repository that are not specific to one of the applications. For example, bugs in mailnews/ Makefiles.
Problems with the writing a new email or replying to one including using the autocomplete feature. Generally, problems found are within the compose window before sending a message. A few examples: 1. User interface and functionality problems with the html compose window and the plain text compose window. 2. Problems with addressing a mail message or adding an attachment.
Problems with underlying code in storage of address book content and mail/news summary files. If the problem you are encountering is with the user interface of the address book or of accessing mail, then this component should not be chosen.
For bugs in MailNews Feed Reader featureset
Problems with using filters to filter your mail. A few examples: 1. User interface and functionality problems with creating, editing, deleting, using filters. 2. Incoming mail is not filtered properly.
Import Mail, Import Mail Settings from third party applications. Also, Import Address Book entries and preferences.
Internationalization is the process of designing and developing a software product to function in multiple locales. This process involves identifying the locales that must be supported, designing features which support those locales, and writing code needed.
Problems with LDAP functionality that relate to mail/news components. For example, performing LDAP queries in the addressbook, LDAP typedown addressing/autocompletion, and LDAP preferences.
Localization is the process of adapting software for a specific international market; this process includes translating the user interface, resizing dialog boxes, replacing icons and other culturally sensitive graphics (if necessary) and customizing features.
Problems with parsing the MIME structure and displaying messages. When this problem happens, it's often useful to attach a copy of the mail message generating the problem. If you have Communicator 4.x, you can select the message and save it as an .eml file (just save with the .eml extension). A few examples: 1. The contents of a message do not display properly. Certain items do not show up.
Problems with getting mail from the user's spool file. (/var/spool/mail/*). This is UNIX only.
Problems with general networking issues integrating with libnet. For specific protocol problems, please choose: IMAP, News, POP, or SMTP from the list.
Problems with receiving mail when your mail account is set up for IMAP. This component should be chosen if you've verified that the receiving problem is specific to IMAP protocol. A few examples: 1. Interoperability problems with IMAP servers (i.e. folders, naming conventions) would fall into this component. 2. Using the IMAP delete model
Problems with reading, posting, or subscribing to newsgroups (also sometimes referred to as USENET)
Problems with receiving mail when your mail account is set up for POP. This component should be chosen if you've verified that the receiving problem is specific to POP protocol. Deleting messages to the trash folder would also fall into this component.
Problems with sending mail. If you have specific problems with the compose window, you should choose the "Composition" component from the list.
Problems with printing mail messages and address book cards.
Problems with migrating your profile from Communicator 4.x to the current Mozilla mail. Choose this component if you've verified that the problem you are seeing does not occur when you create a new profile and add the mail or news account you were using with migration.
Problems with the mail/news search backend
This component covers all bugs that relate to use of cryptography, S/MIME, and SSL issues for MailNews. Or, use this component if you have a MailNews security bug.
S/MIME is the sending of signed and/or encrypted email.
File a bug against this component for problems when using the simple MAPI feature. This feature allows a non-messaging application to perform messaging operations, such as send, address, and receive messages.
Bugs relating to the testing infrastructure that is specific to the mailnews code, e.g. xpcshell-tests, fake servers.