Recs.
Updated
Geary is an email application built around conversations, for the GNOME 3 desktop. It allows you to read, find and send email with a straightforward, modern interface
SpecsUpdate
Pros
Pro SQLite DB for email
It uses SQLite DB for storing email messages from all accounts in one single DB file.
This makes it portable as in you can just copy one SQLite DB file and move your offline mail content to another PC/location. Also, one SQLite DB file for all messages means it is incredibly fast.
Cons
Recommendations
Comments
Flagged Pros + Cons
Pro Native GNOME application
It looks and works like a GNOME application should, so it Just Works™.
Out of Date Pros + Cons
Con No integration with GNOME Online Accounts
Online Accounts integration would allow the user to allow access to the emails in one place only.
Instead you have to login twice if you want to use Online Accounts and Geary.
Con No spellchecking other than English
Yet they are working on it: https://bugzilla.gnome.org/show_bug.cgi?id=720335