FastMail.fm is a SuperFast email system that has few rivals to match its full and fast features.
FastMail, with its 2gig IMAP mailbox on the paid Enhanced account is what Gmail should be and what Yahoo! and Hotmail wish to be: Fast, fat and full of messages!
FastMail offers free accounts and tiered paid accounts but I bought the “Enhanced” $40 a year plan and here’s why:

    2 GB storage space
    1 GB bandwidth per month
    250 MB file space (your own web site)
    IMAP/POP/Web access (IMAP includes clustered folders!)
    SSL IMAP
    SSL SMTP for sending email
    Mail forwarding
    Virus checker; Advanced spam filter
    5 Aliases
    Host your own domain


If you have a lot of email you need to save, search or manage, then you
need the $40 FastMail account. Do not bother with the cheaper or the
free accounts. Go Enhanced and start living again.
FastMail does SSL IMAP and SSL SMTP better than any other company on
the market. Their service is fast. Their web interface is ugly but
really fast. You can search anything you need to find in a FastMail
folder lickety-split!

The greatest thing about FastMail is your ability to create nested IMAP
folders. That means you can have folders within folders within folders
and not all IMAP email systems provide that special feature. Nested
folders allow you to expertly archive your email in folders you may not
immediately need to see or want to see but you know you need to keep.

If you have several email accounts that store old messages, get an
Enhanced FastMail account to unite all your email. Create folders
within folders and stop worrying about running out of space on your
local machine or hitting your quota on your current email system.

Using
an email client like Outlook or Thunderbird will allow you to just drag
and drop messages and entire folders from your current accounts into
your FastMail folders.
FastMail was built to serve you.

What third party email system do you use and like? Are you fawning over
Gmail? Is Yahoo! your thing? Does (storage) size matter? Do you have a
FastMail account? Post a comment and let us know!