Server-side filtering lets you set up rules for deleting certain messages from the server before they are downloaded. Based on the header information, the mailer will delete at the server messages from certain senders, or with certain expressions in the subject field, or with certain addresses in the destination field, etc. Another option is to use a local mail server program such as VPOP3. What's needed are mail clients that let you screen incoming mail based on size, presence of attachments, and whether it is from a known author, etc., downloading only the headers of messages that do not pass your criteria. This can be done to a certain extent by several of the programs, but more satisfactory approaches will be needed in the future.
All mail programs are able to sort incoming mail into folders.
As the screen shots for the individual mailers reviewed here illustrate, messages are typically sorted into separate folders for each mailing list, for different types of content, and for different senders. If you use the same program for both business and personal mail, or if you use more than one mail account, very likely you will want to use different default signatures, reply styles, originating accounts, etc. for different messages. The most convenient way to do this is by setting up different default parameters for each folder. If you use a different folder for each mailing list, for example, originating a message from a specific folder opens a new message with the mailing list address, signature, account and other settings already in place. Controlling the settings for replies and forwarding is also possible, and some mailers even let you control the treatment of mail files on a per-folder basis.