I cannot find a decent offline email client
I spend a lot of time on trains and airplanes without internet connection and keep struggling with the fact that it has become significantly harder to use email without an internet connection. I would like to be able to write a few emails, which would be sent out when I reached civilization and had enough wireless coverage to tether the computer to my phone. Ten years ago, this would have been easy; today, not so much.
(Of course, if there was decent wireless data coverage everywhere, this would not be an issue [1]; except perhaps for data charges. However, as the world stands today, I can get neither a good data connection nor decent software to handle this.)
§
The first email clients were on networked machines are were online only. When dialup came along, they became desktop applications: your mail would be stored on your machine and minimizing the amount of time spent online was often a goal: you would write your messages, save in the Outbox, and then go online to get new messages and send your stored messages. As things moved to the cloud (especially with the appearance of Hotmail and the concept of webmail), desktop email started losing users (it probably never had many customers) and is slowly dying.
I would happily pay for a decent desktop offline-capable email client, but cannot find one. I tried Postbox, but it's just a reheated version of thunderbird. Thunderbird itself is no longer being developed (as Mozilla is focusing on other priorities [2]). I used to use Kmail, which was not great, but worked in KDE3; completely stopped working with the advent of KDE4. Opera Mail is also no longer begin developed.
I could try to use mutt or another command line client, but the command line has not adapted to rich displays [3] and HTML is a nuisance in those [4]. I also enjoy drag&dropping attachments.
§
It is interesting to see how even with software, functionality can be lost if not continuously maintained. [1] Perhaps part of the issue is that the US does have better wireless data coverage than Germany does. Since most technology is developed for that market... [2] I also suspect the technology hit a local maximum and could not easily be improved and the many bugs encountered are very hard to fix. [3] There is no technical reason to not have colour and HTML on the command line, but it's hard to move these very old technology and the track record is that they'll be with us for a few more decades. [4] I still remember when it was considered rude by some to send HTML email. I too had a phase like that.