MailDroid is an ad-supported Webdav/POP3/IMAP Idle Push mail client written from the ground up and and not based on the stock Android email client.
MailDroid has all the features you could want from a mobile email client and it continues to be built around user feedback. With the ability for IMAP users to sync draft mails, sent mail, deleted mail based on when they are on wifi or mobile as well as pop3 preload capability, MailDroid was built with mobile data in mind from the start. MailDroid also is an email client focusing in on what business users want such as choosing to delete an email locally or from both device and server per email read as well as custom rules to alert and move certain email to folders. Finally, for the power users there is even encryption capability using open PGP and S/MIME. MailDroid will allow you to encrypt and/or sign email using open PGP in the MIME format or Inline format and allow you to encrypt and/or sign an email using S/MIME. There are so many other features that can be found in the app, see a sample below:
Permissions needed for Ads
1. Complete email re-write and not based at all on the standard Android mail client
2. IMAP Idle Push for all IMAP email servers that support it (including, Hotmail, Outlook, Yahoo, Aol, FastMail, GMX and many more)
3. Save/Download Attachments from email to SD card using ES Explorer, Astro, or any other file explorer. You can also use the built in File Manager.
4. Settings Support for signature, font size, ring tone, led color, icon selection etc.
5. Custom Mail Rules (like outlook and thunderbird)
6. Spell Check
7. Search your mail online (for IMAP only) or offline for both IMAP and POP
8. Password Protection
9. Microsoft Exchange 2003,2007,2010, Office 365
10. Full WYSIWYG editor
11. Split screen for tablets
12. Calendar integration using ICS attachment for IMAP and POP (exchange 2007/2010 support is coming)
13. Cloud storage integration (dropbox, box.net, google drive)
14. Customize your inbox styles to your preference
15. Spam Filter Plugin ==> REQUIRES AN IN-APP PAYMENT
16. Email Conversation Threaded Mode
17. Mobile View options
18. Different notification styles and icons
19. Identities or Aliases
20. Backup SMTP Provider capability
21. open PGP support using PGP Inline or PGP MIME
22. S/MIME support
23. Custom themes using the MailDroid Theme Plugin
24. Much more....
PLEASE NOTE THAT ACTIVESYNC IS NOT SUPPORTED AT THIS TIME!
PLEASE NOTE THAT SPAM SUBSCRIPTIONS DO NOT CARRY OVER TO THE PRO VERSION.
Please email support if you have any questions or see any issues.
Please read this for a better explanation of what we did with ads http://goo.gl/DO4UBQ
+ Two permissions added to allow for users on Android 4.0+ who use the new Google File picker to attach files
+ Option to set your desired account to use to encrypt
+ Choose a default S/MIME or PGP
+ Fixed a number of S/MIME and PGP issues (please update the crypto plugin)
+ Fixed an issue with Google Drive
+ Fixed some MIME validation issues