Descriptions : K + 9 Mail is an open source email client with support for multiple accounts, search, IMAP push email, multiple folder sync, tag, file, signatures, BCC + self, PGP / MIME and more !
K + 9 supports IMAP, POP3 and Exchange 2003/2007 (with WebDAV).
Required Android Versions : Ice Cream Sandwich [4.0.3–4.0.4] - Jelly Bean [4.1–4.3.1] - KitKat [4.4–4.4.4] - Lollipop [5.0–5.0.2] - Marshmallow [6.0 - 6.0.1] - Nougat [7.0 – 7.1.1] - Oreo [8.0-8.1]