ProfiMail

"ProfiMail is a powerful e-mail client for mobile devices. It allows you to read your mail on go,
and send text with attachments directly from your device.

Features:

• Automatic synchronization of messages with mail server
• IMAP folders
• Attachments - view, save, send
• HTML messages with images and hyperlinks
• Built-in File Explorer
• Address book
• Signatures
• Support for POP3 / IMAP / SMTP mail servers
• Writing mails using T9 dictionary
• Multiple email accounts
• Rules and filters allowing selective message download
• Opens and browses ZIP archives
• Support for various character encoding - Western, Cyrillic, Central European, and more
• Build-in image viewer - JPG, PNG and other popular formats
• Text viewer for standard text, HTML and Word documents
• Optimized for GPRS - get headers first, then download message bodies which you really want to see
• Scheduled message download
• Sound notifications"

For sure the best mail client for Symbian ( Series60, Series80 and UIQ; also work on Windows Mobile SmartPhone and Pocket PC )
You can get if from LonelyCatGames